Absorbent articles with improved absorption properties

ABSTRACT

An absorbent article such as disposable diaper, training pant, and adult incontinence undergarment comprising an absorbent structure comprising superabsorbent polymer particles, the article being able to absorb and contain body exudates and having improved absorption properties and therefore being able to reduce leakage, especially at the first gush, i.e. when the article starts to be wetted.

FIELD OF THE INVENTION

The present invention is directed to absorbent articles such asdisposable diapers, training pants and adult incontinence undergarmentscomprising superabsorbent polymer particles.

BACKGROUND OF THE INVENTION

Absorbent articles, such as disposable diapers, training pants, andadult incontinence undergarments, absorb and contain body exudates. Manyabsorbent articles, like diapers, contain superabsorbent polymermaterial. Superabsorbent polymers are typically present in the core ofthe absorbent articles in the form of particles. Superabsorbent polymerparticles are able to absorb liquid and swell when entering into contactwith liquid exudates. However, it has been shown in the past that notall categories of superabsorbent polymer particles are equally suitablefor use in an absorbent article.

It is known that in order to have absorbent articles comprisingsuperabsorbent polymer particles which exhibit good absorbing andcontaining functions, specific technical requirements need to befulfilled by the superabsorbent polymer particles.

The superabsorbent polymer particles need first to be able to absorb theliquid exudates fast. The absorption speed of superabsorbent polymerparticles has generally been characterized in the prior art by measuringthe Free Swell Rate (FSR) of the particles.

In addition to having a high absorption speed, the superabsorbentpolymer particles present in the core need to be also highly permeableto liquid. A poor permeability of the superabsorbent polymer particlesmay induce leakage of the absorbent article due to gel blocking Gelblocking can occur in the absorbent core when swelling superabsorbentpolymer particles block the void spaces between the particles. In such acase, the liquid exudates can not or only slowly reach underneath layersof superabsorbent polymer particles disposed in the core. The liquidexudates remain on the surface of the absorbent core and may thereforeleak from the diaper.

The permeability of the superabsorbent polymer particles has typicallybeen characterized in the prior art by measuring the SFC (Saline FlowConductivity) of the particles. This parameter is measured atequilibrium, i.e. the measure is performed on a fully preswollen gel bedof superabsorbent polymer particles.

However, the inventors have now surprisingly found that absorbent corescomprising superabsorbent polymer particles having high FSR and high SFCvalues do not automatically conduct to fast acquisition times of liquidexudates into the absorbent article, especially at the first gush, i.e.when the absorbent cores first come into contact with liquid.

The present invention therefore provides an absorbent article havingimproved absorption properties and therefore reduced leakage, especiallyat the first gush, i.e. when the article starts to be wetted.

SUMMARY OF THE INVENTION

The present invention relates to an absorbent article comprising anabsorbent structure. The absorbent article is divided into threeportions: a front portion, a back portion and a crotch portion disposedbetween the front portion and the back portion. The absorbent structurecomprises an absorbent core. The absorbent core has a dry thickness atthe crotch point of the article of from 0.2 to 5 mm. One or moreportion(s) of the absorbent structure comprise(s) at least 90% by weightof superabsorbent polymer particles and require(s) a time to reach anuptake of 20 g/g (T20) of less than 440 s as measured according to theK(t) test method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a diaper in accordance with an embodiment ofthe present invention.

FIG. 2 is a cross sectional view of the diaper shown in FIG. 1 takenalong the sectional line 2-2 of FIG. 1.

FIG. 3 is a partial cross sectional view of an absorbent core layer inaccordance with an embodiment of this invention.

FIG. 4 is a partial cross sectional view of an absorbent core layer inaccordance with another embodiment of this invention.

FIG. 5 a is a partial sectional view of an absorbent core comprising acombination of the first and second absorbent core layers illustrated inFIGS. 3 and 4.

FIG. 5 b is a partial sectional view of an absorbent core comprising acombination of the first and second absorbent core layers illustrated inFIGS. 3 and 4.

FIG. 6 is a schematic representation of a rheometer.

FIG. 7 is a partial cross-sectional side view of a suitable permeabilitymeasurement system for conducting the Dynamic Effective Permeability andUptake Kinetics Measurement Test.

FIG. 8 is a cross-sectional side view of a piston/cylinder assembly foruse in conducting the Dynamic Effective Permeability and Uptake KineticsMeasurement Test

FIG. 9 is a top view of a piston head suitable for use in thepiston/cylinder assembly shown in FIG. 8.

FIG. 10 is a partial cross-sectional side view of a suitablepermeability measurement system for conducting the Urine PermeabilityMeasurement Test.

FIG. 11 is a cross-sectional side view of a piston/cylinder assembly foruse in conducting the Urine Permeability Measurement Test.

FIG. 12 is a top view of a piston head suitable for use in thepiston/cylinder assembly shown in FIG. 11.

FIG. 13 is a cross-sectional side view of the piston/cylinder assemblyof FIG. 11 placed on fitted disc for the swelling phase.

FIG. 14 is a cross-sectional view of a suitable Flat Acquisitionmeasurement system for conducting the Flat Acquisition Test

FIG. 15 is a cross-sectional view of an absorbent structure to be testedaccording to the K(t) Test Method wherein a layer of material which isnot part of the absorbent structure is removed from the absorbentstructure with the aid of a Cold Spray

FIG. 16 is a cross-sectional view of an absorbent structure to be testedaccording to the K(t) Test Method wherein the upper layer of theabsorbent structure is perforated using a perforating tip.

FIG. 17 is a top view of the perforation pattern according to which theupper or lower layer of an absorbent structure can be perforated.

FIG. 18A is a graphic representing the uptake in g/g as a function oftime for the absorbent structures of the comparative examples 1 and 2and of Example 1 as measured according to the K(t) Test Method.

FIG. 18B is a graphic representing the uptake in g/g as a function oftime for the absorbent structures of the comparative examples 1 and 2and of Example 2 as measured according to the K(t) Test Method.

DETAILED DESCRIPTION OF THE INVENTION

Absorbent article” is used herein to refer to devices that absorb andcontain body exudates, and, more specifically, refers to devices thatare placed against or in proximity to the body of the wearer to absorband contain the various exudates discharged from the body. Absorbentarticles include diapers, training pants, adult incontinenceundergarments, feminine hygiene products and the like. As used herein,the term “body fluids” or “body exudates” includes, but is not limitedto, urine, blood, vaginal discharges, breast milk, sweat and fecalmatter. In some embodiments of the present invention, the absorbentarticle is a diaper or training pant.

“Absorbent core” is used herein to refer to a structure disposed betweena topsheet and a backsheet of an absorbent article for absorbing andcontaining liquid received by the absorbent article. The core comprisessuperabsorbent polymer particles. The core may comprise one or moresubstrate layer(s), superabsorbent polymer particles disposed on the oneor more substrate layer(s), and a thermoplastic composition typicallydisposed on the superabsorbent polymer particles. Typically thethermoplastic composition is a thermoplastic adhesive material. Thethermoplastic adhesive material may form a fibrous layer which is atleast partially in contact with the superabsorbent polymer particles onthe one or more substrate layers and partially in contact with the oneor more substrate layers. Auxiliary adhesive may be deposited on the oneor more substrate layers before application of the superabsorbentpolymer particles for enhancing adhesion of the superabsorbent polymerparticles and/or of the thermoplastic adhesive material to therespective substrate layer(s). The absorbent core may also include oneor more cover layer(s) such that the superabsorbent polymer particlesare disposed between the one or more substrate layer(s) and the one ormore cover layer(s). The one or more substrate layer(s) or coverlayer(s) may comprise or consist of a nonwoven, a tissue or a film orcombinations thereof. The absorbent core may further comprise odorcontrol compounds.

The absorbent core may consist essentially of the one or more substratelayer(s), the superabsorbent polymer particles, the thermoplasticcomposition, optionally the auxiliary adhesive, optionally the coverlayer(s), and optionally odor control compounds.

The absorbent core may comprise superabsorbent polymer particles whichare sandwiched between two layers namely an upper layer and a lowerlayer with no superabsorbent polymer particles above the upper layer andbelow the lower layer. The upper layer corresponds to the substratelayer or cover layer of the absorbent core which is closest to thetopsheet of the article and the lower layer corresponds to the substratelayer or cover layer of the absorbent core which is closest to thebacksheet of the absorbent article. Alternatively, in the absence of anupper layer, the absorbent core may correspond to the structure which isdisposed between the topsheet and the lower layer or in the absence of alower layer, the absorbent core may correspond to the structure which isdisposed between the upper layer and the backsheet. In the absence anupper layer and a lower layer, the absorbent core may correspond to thewhole structure which is disposed between the topsheet and the backsheetof the absorbent article. The substrate layer(s) or cover layer(s) maycomprise or consist of a nonwoven, a tissue or a film or combinationsthereof.

“Absorbent structure” is used herein to refer to one of the followingstructures:

-   -   a. the absorbent core of the absorbent article in case the        absorbent core comprises superabsorbent polymer particles which        are sandwiched between two layers namely an upper layer and a        lower layer with no superabsorbent polymer particles above the        upper layer and below the lower layer. The upper layer        corresponds to the substrate layer or cover layer of the        absorbent core being closest to the topsheet of the article and        the lower layer corresponds to the substrate layer or cover        layer of the absorbent core being closest to the backsheet of        the absorbent article    -   b. the absorbent core of the absorbent article in combination        with the topsheet of the absorbent article in case the absorbent        core does not comprise an upper layer as defined hereinbefore    -   c. the absorbent core of the absorbent article in combination        with the backsheet of the absorbent article in case the        absorbent core does not comprise a lower layer as defined        hereinbefore

“Portion of the absorbent structure” is used herein to refer to aportion of the absorbent structure through the thickness of theabsorbent structure, i.e. a portion of the absorbent structurecomprising all the different layers the absorbent structure is made ofin the respective portion.

“Front portion” and “back portion” is used herein to refer to the frontand back waist regions of the absorbent article. The length of both thefront portion and the back portion is one third of the overall length ofthe article starting at the respective front and back waist edges. Forembodiments, wherein the front and/or back waist edge is/are notconfigured as a straight line extending in parallel to the transversecenterline of the absorbent article, the length of the absorbent articleis determined on or parallel to the longitudinal centerline by startingfrom the point of the front waist edge which is closest to thetransverse centerline and terminating at the point of back waist edgewhich is closest to the transverse centerline.

“Crotch portion” is used herein to refer to the region of the articlepositioned in the center of the article between the front and the backportion of the article. The length of the crotch portion is one third ofthe overall length of the article.

“Crotch point” is used herein to refer to the point of the article whichis positioned in the center of the absorbent article at the intersectionof the longitudinal centerline and the transverse centerline of thearticle. It should be understood for the purpose of the invention thatthe crotch point of the article is not necessarily positioned in thecenter of the absorbent core, namely at the intersection of thelongitudinal centerline and the transverse centerline of the absorbentcore, especially in case the absorbent core is not centered on thetransverse centerline of the article, i.e. in case the absorbent core isshifted to the front and/or the back of the article.

“Center of the front portion” is used herein to refer to the point ofthe absorbent article which is positioned at the intersection of thelongitudinal centerline of the article and the line which is parallel tothe transverse centerline of the article and positioned at a distancefrom the transverse centerline of one third of the overall length of theabsorbent article. For embodiments, wherein the front and/or back waistedge is/are not configured as a straight line extending in parallel tothe transverse centerline of the absorbent article, the length of theabsorbent article is determined on or parallel to the longitudinalcenterline by starting from the point of the front waist edge which isclosest to the transverse centerline and terminating at the point ofback waist edge which is closest to the transverse centerline.

“Comprise,” “comprising,” and “comprises” are open ended terms whichalso encompass the terms “consist of”, “consisting of” or “consists of”which are closed ended terms.

“Airfelt” is used herein to refer to comminuted wood pulp, which is aform of cellulosic fiber.

“Superabsorbent polymer particle” is used herein to refer to crosslinked polymeric materials that can absorb at least 10 times theirweight of an aqueous 0.9% saline solution as measured using theCentrifuge Retention Capacity test (EDANA WSP 241.2-05). Thesuperabsorbent polymer particles are in particulate form so as to beflowable in the dry state. Preferred superabsorbent polymer particles ofthe present invention are made of poly(meth)acrylic acid polymers.However, e.g. starch-based superabsorbent polymer particles are alsowithin the scope of the present invention

“Thermoplastic adhesive material” is used herein to refer to a polymercomposition from which fibers may be formed and applied to thesuperabsorbent polymer particles with the intent to immobilize thesuperabsorbent polymer particles in both the dry and wet state. Thethermoplastic adhesive material of the present invention preferablyforms a fibrous network over the superabsorbent polymer particles.

A “nonwoven” is used herein to refer to a manufactured sheet, web orbatt of directionally or randomly orientated fibers, bonded by friction,and/or cohesion and/or adhesion, excluding paper and products which arewoven, knitted, tufted, stitch-bonded incorporating binding yarns orfilaments, or felted by wet-milling, whether or not additionallyneedled. The fibers may be of natural or man-made origin and may bestaple or continuous filaments or be formed in situ. Commerciallyavailable fibers have diameters ranging from less than about 0.001 mm tomore than about 0.2 mm and they come in several different forms: shortfibers (known as staple, or chopped), continuous single fibers(filaments or monofilaments), untwisted bundles of continuous filaments(tow), and twisted bundles of continuous filaments (yarn). Nonwovenfabrics can be formed by many processes such as meltblowing,spunbonding, solvent spinning, electrospinning, and carding. The basisweight of nonwoven fabrics is usually expressed in grams per squaremeter (gsm).

“Attached” is used herein to refer to configurations whereby a firstelement is directly secured to another element by affixing the firstelement directly to a second element or whereby a first element isindirectly secured to a second element by affixing the first element toa third, intermediate member(s), which in turn are affixed to the secondelement. The attachment means may comprise adhesive bonds, heat bonds,pressure bonds, ultrasonic bonds, dynamic mechanical bonds, or any othersuitable attachment means or combinations of these attachment means asare known in the art.

FIG. 1 is a plan view of an absorbent article 10 according to someembodiments of the present invention. The absorbent article 10 is shownin its flat out, uncontracted state (i.e., without elastic inducedcontraction) and portions of the absorbent article 10 are cut away tomore clearly show the underlying structure of the diaper 10. A portionof the absorbent article 10 that contacts a wearer is facing the viewerin FIG. 1. The absorbent article 10 generally comprises a chassis 12 andan absorbent core 14 disposed in the chassis 12.

The chassis 12 of the absorbent article 10 in FIG. 1 may comprise themain body of the absorbent article 10. The chassis 12 may comprise anouter covering 16 including a topsheet 18, which may be liquid pervious,and/or a backsheet 20, which may be liquid impervious. The absorbentcore 14 may be encased between the topsheet 18 and the backsheet 20. Thechassis 12 may also include side panels 22, elasticized leg cuffs 24,and an elastic waist feature 26.

The leg cuffs 24 and the elastic waist feature 26 may each typicallycomprise elastic members 28. One end portion of the absorbent article 10is configured as the front portion 30 and the other end portion isconfigured as the back portion 32 of the absorbent article 10. Theintermediate portion of the absorbent article 10 is configured as thecrotch portion 34, which extends longitudinally between the front andthe back portions 30 and 32.

The absorbent article 10 is depicted in FIG. 1 with its longitudinalcenterline 36 and its transverse centerline 38. The periphery 40 of theabsorbent article 10 is defined by the outer edges of the absorbentarticle 10 in which the longitudinal edges 42 run generally parallel tothe longitudinal centerline 36 of the absorbent article 10 and the frontand back waist edges 43 and 44 run between the longitudinal edges 42generally parallel to the transverse centerline 38 of the absorbentarticle 10. The chassis 12 may also comprise a fastening system, whichmay include at least one fastening member 46 and at least one landingzone 48.

The absorbent article 10 may also include such other features as areknown in the art including front and rear ear panels, waist capfeatures, elastics and the like to provide better fit, containment andaesthetic characteristics. Such additional features are well known inthe art and are e.g., described in U.S. Pat. No. 3,860,003 and U.S. Pat.No. 5,151,092.

In order to keep the absorbent article 10 in place about the wearer, atleast a portion of the front portion 30 may be attached by the fasteningmember 46 to at least a portion of the back portion 32 to form legopening(s) and an article waist. When fastened, the fastening systemcarries a tensile load around the article waist. The fastening systemmay allow an article user to hold one element of the fastening system,such as the fastening member 46, and connect the front portion 30 to theback portion 32 in at least two places. This may be achieved throughmanipulation of bond strengths between the fastening device elements.

According to certain embodiments, the absorbent article 10 may beprovided with a re-closable fastening system or may alternatively beprovided in the form of a pant-type diaper. When the absorbent articleis a diaper, it may comprise a re-closable fastening system joined tothe chassis for securing the diaper to a wearer. When the absorbentarticle is a pant-type diaper, the article may comprise at least twoside panels joined to each other to form a pant.

The Absorbent Structure

The absorbent structure comprises superabsorbent polymer particles.

One or more portion(s) of the absorbent structure comprises at least 90%by weight of superabsorbent polymer particles based on the weight of theportion of the absorbent structure, excluding the weight of anysubstrate layer and/or cover layer and/or topsheet and/or backsheet thatmight be included in the portion of the absorbent structure. The one ormore substrate layer(s) or cover layer(s) may comprise or consist of anonwoven, a tissue or a film, or combinations thereof.

One of the one or more portion(s) of the absorbent structure may becentered on the center of the front portion of the article and/or one ofthe one or more portion(s) of the absorbent structure may be centered onthe crotch point of the article.

At least one of the one or more portion(s) of the absorbent structuremay have a surface area of 30 cm² or more. Alternatively, each of theone or more portion(s) may have a surface area of 30 cm² or more.

At least one of the one or more portion(s) of the absorbent structurehaving a surface area of 30 cm² or more may encompass a circular area.Alternatively, each of the one or more portion(s) of the absorbentstructure having a surface area of 30 cm² or more may encompass acircular area.

The one or more portion(s) of the absorbent structure may comprise atleast 95% by weight of superabsorbent polymer particles.

The one or more portion(s) of the absorbent structure may comprise atleast 98% by weight of superabsorbent polymer particles.

The one or more portion(s) of the absorbent structure may comprise atleast 99% by weight of superabsorbent polymer particles.

The whole absorbent structure may comprise at least 90% by weight,preferably at least 95% by weight, more preferably at least 98% byweight, even more preferably at least 99% by weight of superabsorbentpolymer particles.

These embodiments are particularly preferred since absorbent articlescomprising a high percentage of superabsorbent polymer particlestypically have a reduced thickness when dry in comparison with thethickness of conventional absorbent articles having a higher amount ofconventional absorbent materials, such as airfelt and the like inaddition to the superabsorbent polymer particles. The reduced thicknesshelps to improve the fit and the comfort when the article is positionedon the wearer.

The one or more portion(s) of the absorbent structure require a time toreach an uptake of 20 g/g (T20) of less than 440 s, or less than 400 s,or less than 350 s, or less than 300 s, or less than 250 s as measuredaccording to the K(t) test method set out below.

The time to reach an uptake of 20 g/g (T20) may be of 50 s to 440 s, or100 s to 350 s, or 150 s to 300 s, as measured according to the K(t)test method set out below.

The one or more portion(s) of the absorbent structure may have aneffective permeability at 20 minutes (K20) of at least 2.9.10⁻⁸ cm² asmeasured according to the K(t) test method.

The one or more portion(s) of the absorbent structure may have aneffective permeability at 20 minutes (K20) of at least 2.95·10⁻⁸ cm², orat least 3·10⁻⁸ cm², or of 2.95·10⁻⁸ cm² to 1.0·10⁻⁶ cm², or of2.95·10⁻⁸ cm² to 1.0·10⁻⁷ cm², or of 3.0·10⁻⁸ to 1.0·10⁻⁷ cm² asmeasured according to the K(t) test method set out below.

The one or more portion(s) of the absorbent structure may have a ratiobetween the minimum effective permeability and the permeability at 20minutes (Kmin/K20 ratio) of more than 0.75, or more than 0.8 or morethan 0.9 as measured according to the K(t) test method set out below. Insuch embodiments the transient gel blocking is minimum and the liquidexudates are able to travel fast through the void spaces present betweenthe particles throughout all the swelling process and especially in theinitial part of the swelling phase which is the most critical for thefirst gush.

The uptake of the one or more portion(s) of the absorbent structure at20 min (U20) is of at least 24 g/g or at least 24.5 g/g, or of 24 g/g to60 g/g, or of 24.5 g/g to 50 g/g, or of 24.5 g/g to 40 g/g as measuredaccording to the K(t) test method set out below.

In some embodiments, the whole absorbent structure meets the T20, K20and U20 values mentioned hereinbefore.

Absorbent articles comprising such an absorbent structure have improvedabsorption properties and therefore exhibit reduced leakage incomparison with absorbent articles of the prior art, especially at thefirst gush. Such absorbent structures are particularly suitable for usein absorbent articles.

The Absorbent Core

In some embodiments, the absorbent core comprises an average amount ofsuperabsorbent polymer particles per area of from 50 to 2200 g/m² or 100to 1500 g/m² or 200 to 1000 g/m².

In some embodiments, the absorbent core comprises an average amount ofsuperabsorbent polymer particles per area of from 100 to 1500 g/m², or150 to 1000 g/m², or 200 to 900 g/m², or 400 to 700 g/m² in the crotchportion of the article. The absorbent article comprises enough amount ofsuperabsorbent polymer particles to have good absorption properties aswell as to be sufficient thin to provide fit and comfort to the wearer.However, superabsorbent polymer particles are also present in the frontand back portions, though especially in back portion amount may be low(or even zero). In some embodiments, the absorbent core comprises anaverage amount of superabsorbent polymer particles per surface area ofless than 300 g/m², or less than 200 g/m², alternatively from 25 to 300g/m², or 50 to 200 g/m² or 50 to 100 g/m² in the back portion of thearticle.

In some embodiments, the absorbent core may further comprise minoramounts of an absorbent material other than superabsorbent polymerparticles, e.g. airfelt.

In some embodiments, the absorbent core typically comprises less than 5%by weight of airfelt, preferably less than 2% and more preferably isairfelt free. In some embodiments, the absorbent structure can also beairfelt free.

The absorbent core has a dry thickness at the crotch point of thearticle of less than 10 mm, preferably less than 5 mm, more preferablyless than 3 mm, even more preferably less than 1.5 mm, alternativelyfrom 0.1 to 10 mm, preferably from 0.2 to 5 mm, more preferably from 0.3to 3 mm, even more preferably from 0.5 to 1.5 mm, as measured accordingto the test method set out below. The absorbent core is thussufficiently thin compared to conventional airfelt containing absorbentcores. Thereby, fit and comfort is substantially improved.

The Superabsorbent Polymer Particles

The superabsorbent polymer particles useful for the present inventionmay be of numerous shapes. The term “particles” refers to granules,fibers, flakes, spheres, powders, platelets and other shapes and formsknown to persons skilled in the art of superabsorbent polymer particles.In some embodiments, the superabsorbent polymer particles can be in theshape of fibers, i.e. elongated, acicular superabsorbent polymerparticles. In those embodiments, the superabsorbent polymer particlesfibers have a minor dimension (i.e. diameter of the fiber) of less thanabout 1 mm, usually less than about 500 μm, and preferably less than 250μm down to 50 μm. The length of the fibers is preferably about 3 mm toabout 100 mm. The fibers can also be in the form of a long filament thatcan be woven.

Alternatively, in some preferred embodiments, superabsorbent polymerparticles of the present invention are spherical-like particles.According to the present invention and in contrast to fibers,“spherical-like particles” have a longest and a smallest dimension witha particulate ratio of longest to smallest particle dimension in therange of 1-5, where a value of 1 would equate a perfectly sphericalparticle and 5 would allow for some deviation from such a sphericalparticle. In such embodiments, the superabsorbent polymer particles mayhave a particle size of less than 850 μm, or from 50 to 850 μm,preferably from 100 to 500 μm, more preferably from 150 to 300 μm, asmeasured according to EDANA method WSP 220.2-05. Superabsorbent polymerparticles having a relatively low particle size help to increase thesurface area of the absorbent material which is in contact with liquidexudates and therefore support fast absorption of liquid exudates.

The superabsorbent polymer particles useful in the present inventioninclude a variety of water-insoluble, but water-swellable polymerscapable of absorbing large quantities of fluids. Such polymers materialsare generally known in the art.

Suitable superabsorbent polymer particles may for example be obtainedfrom inverse phase suspension polymerizations as described in U.S. Pat.No. 4,340,706 and U.S. Pat. No. 5,849,816 or from spray- or othergas-phase dispersion polymerizations as described in U.S. PatentApplications No. 2009/0192035, 2009/0258994 and 2010/0068520. In someembodiments, suitable superabsorbent polymer particles may be obtainedby current state of the art production processes as is more particularlydescribed from page 12, line 23 to page 20, line 27 of WO 2006/083584.

In some embodiments, the surface of the superabsorbent polymer particlesmay be coated. In such embodiments, the coating makes surface sticky sothat superabsorbent polymer particles cannot rearrange (so they cannotblock voids) easily upon wetting.

In some embodiments, the superabsorbent polymer particles may be coatedwith a cationic polymer. Preferred cationic polymers can includepolyamine or polyimine materials which are reactive with at least onecomponent included in body fluids, especially in urine. Preferredpolyamine materials are selected from the group consisting of (1)polymers having primary amine groups (e.g., polyvinylamine, polyallylamine); (2) polymers having secondary amine groups (e.g.,polyethyleneimine); and (3) polymers having tertiary amine groups (e.g.,poly N,N-dimethylalkyl amine).

Practical examples of the cationic polymer are, for example,polyethyleneimine, a modified polyethyleneimine which is crosslinked byepihalohydrine in a range soluble in water, polyamine, a modifiedpolyamidoamine by graft of ethyleneimine, polyetheramine,polyvinylamine, polyalkylamine, polyamidopolyamine, and polyallylamine.

In preferred embodiments, a cationic polymer has a weight-averagemolecular weight of at least 500, more preferably 5,000, most preferably10,000 or more. Cationic polymers having a weight-average molecularweight of more than 500 or more are not limited to polymers showing asingle maximum value (a peak) in a molecular weight analysis by gelpermeation chromatography, and polymers having a weight-averagemolecular weight of 500 or more may be used even if it exhibits a pluralmaximum value (peaks).

A preferable amount of the cationic polymer is in a range of from about0.05 to 20 parts by weight against 100 parts by weight of thesuperabsorbent polymer particle, more preferably from about 0.3 to 10parts by weight, and most preferably from about 0.5 to 5 parts byweight.

In some embodiments, the superabsorbent polymer particles may be coatedwith chitosan materials such as the one disclosed in U.S. Pat. No.7,537,832 B2.

In some other embodiments, the superabsorbent polymer particles maycomprise mixed-bed Ion-Exchange absorbent polymers such as the onedisclosed in WO 99/34841 and WO 99/34842.

As already mentioned above, absorbent structures comprisingsuperabsorbent polymer particles having high SFC and FSR values do notautomatically lead to fast acquisition times of liquid exudates,especially at the first gush, i.e. when the dry absorbent structurescome into contact with liquid. Without being bound by theory it isthought that dry superabsorbent polymer particles are typically morereluctant to absorb water than wetted superabsorbent polymer particlessince the diffusivity of water into dry superabsorbent polymer particlesis lower than the diffusivity of water into wetted superabsorbentpolymer particles.

Hitherto, absorption properties of dry absorbent structures comprisingsuperabsorbent polymer particles related to the initial uptake has notbeen investigated. Rather, the focus has been on Saline FlowConductivity (SFC) of the superabsorbent polymer particles, which isdetermined at equilibrium and thus at a stage remote from initial liquiduptake. For absorbent structures containing a significant amount ofairfelt in addition to superabsorbent polymer particles, temporarystorage of liquid entering the absorbent core is provided by the airfeltallowing the superabsorbent polymer particles to absorb liquid from thesurrounding airfelt with a certain delay. But even for airfelt freeabsorbent articles disclosed in the prior art, permeability of thesuperabsorbent polymer particles has always been measured atequilibrium, thus not taking into account the behaviour of drysuperabsorbent polymer particles upon initial exposure to liquid. Theinventors of the present invention have carefully investigated thebehaviour of absorbent structures comprising superabsorbent polymerparticles upon initial exposure to liquid. They have found that certain,not yet publicly available absorbent structures comprisingsuperabsorbent polymer particles and no or very low amounts of airfeltexhibit superior performance. The superior performance has lead toimproved liquid acquisition, thus reducing the risk of leakage. It hasbeen found that superior absorbent structures comprising superabsorbentpolymer particles can be described in terms of the time it takes for dryabsorbent structures comprising superabsorbent polymer particles toreach a certain liquid uptake when absorbing against a confiningpressure. Thereby, it is now possible to purposefully and easily selectthese newly developed absorbent structures, without the need foradditional extensive investigation and testing.

In some embodiments, the absorbent structure comprises superabsorbentpolymer particles having a permeability at equilibrium expressed as UPM(Urine Permeability Measurement) value of more than 50, preferably morethan 60, or of 50 to 500, or of 55 to 200, or of 60 to 150 UPM units,where 1 UPM unit is 1×10⁻⁷ (cm³.s)/g.

The UPM value is measured according to the UPM Test method set outbelow. This method is closely related to the SFC test method of theprior art. The UPM Test method typically measures the flow resistance ofa preswollen layer of superabsorbent polymer particles, i.e. the flowresistance is measured at equilibrium. Therefore, such superabsorbentpolymer particles having a high UPM value exhibit a high permeabilitywhen a significant volume of the absorbent article is already wetted bythe liquid exudates. Absorbent structures comprising such superabsorbentpolymer particles exhibit good absorption properties not only at thefirst gush but also at the subsequent gushes.

In some embodiments, the absorbent structure may comprise superabsorbentpolymer particles having a FSR (Free Swell Rate) of more than 0.1 g/g/s,or of from 0.1 to 2 g/g/s, or 0.3 to 1 g/g/s, or 0.3 to 0.6 g/g/s, or0.4 to 0.6 g/g/s.

The Free Swell Rate of the superabsorbent polymer particles is measuredaccording to the FSR test method set out below. Absorbent structurescomprising superabsorbent polymer particles having high free swell ratevalues will be able to absorb liquid quickly under no confiningpressure. Contrary to the K(t) test method, no external pressure isapplied to the gel bed in order to measure the free swell rate.Absorbent structures comprising superabsorbent polymer particles havinga too low FSR value may not require less than 440 s to reach an uptakeof 20 g/g as measured according to the K(t) test method of the presentinvention and will consequently not be able to absorb the liquidexudates as fast as necessary. However, as stated above, absorbentstructures comprising superabsorbent polymer particles having a high FSRvalue do not automatically lead to high uptake values as measuredaccording to the K(t) test method.

In some embodiments, the absorbent structure may comprise superabsorbentpolymer particles having a CRC (centrifuge retention capacity) value ofmore than 20 g/g, or more than 24 g/g, or of from 20 to 50 g/g, or 20 to40 g/g, or 24 to 30 g/g, as measured according to EDANA method WSP241.2-05. The CRC measures the liquid absorbed by the superabsorbentpolymer particles for free swelling in excess liquid. Absorbentstructures comprising superabsorbent polymer particles having a high CRCvalue are preferred since less superabsorbent polymer particles areneeded to facilitate a required overall capacity for liquid absorption.

In some embodiments, the absorbent article may have an acquisition timefor the first gush of less than 30 s, preferably less than 27 s, asmeasured according to the Flat Acquisition test method set out below.This acquisition time is measured on a baby diaper which is designatedfor wearers having a weight in the range of 8 to 13 kg±20% (such asPampers Active Fit size 4 or other Pampers baby diapers size 4, Huggiesbaby diapers size 4 or baby diapers size 4 of most other tradenames). Anabsorbent article comprising an absorbent structure which comprisessuperabsorbent polymer particles and requires less than 440 s to reachan uptake of 20 g/g as measured according to the K(t) test method canprovide faster acquisition times, especially at the first gush and thusreduced leakage, in comparison with the absorbent articles of the priorart, as shown in the Examples section of the application.

Structure of the Absorbent Core

In the following, an example for an absorbent core of the presentinvention is given. The present invention is however not limited to suchabsorbent cores.

In some embodiments, the absorbent core 14 comprises an absorbent layer60, as illustrated in FIGS. 3 and 4. The substrate layer 64 of theabsorbent layer 60 may be referred to as a dusting layer and has a firstsurface 78 which faces the backsheet 20 of the diaper 10 and a secondsurface 80 which faces the superabsorbent polymer particles 66.According to some embodiments, the substrate layer 64 is a non-wovenmaterial such as a multi-layered nonwoven material having spunbondedlayers as outer layers and one or more meltblown layers inbetween thespunbond layers, including but not limited to SMS material, comprising aspunbonded, a melt-blown and a further spunbonded layer. The absorbentlayer 60 may include a cover layer 70 as illustrated in FIG. 4. Thecover layer 70 may be a non-woven material such as a multi-layerednonwoven material having spunbonded layers as outer layers and one ormore meltblown layers inbetween the spunbond layers, including but notlimited to SMS material, comprising a spunbonded, a melt-blown and afurther spunbonded layer. In some embodiments, the substrate layer 64and the cover layer 70 are made of the same material.

As illustrated in FIGS. 3 and 4, the superabsorbent polymer particles 66can be deposited on the substrate layer 64 in clusters 90 of particlescomprising land areas 94 and junction areas 96 between the land areas94. As defined herein, land areas 94 are areas where the thermoplasticadhesive material does not contact the nonwoven substrate or theauxiliary adhesive directly; junction areas 96 are areas where thethermoplastic adhesive material does contact the nonwoven substrate orthe auxiliary adhesive directly. The junction areas 96 contain little orno superabsorbent polymer particles 66. The land areas 94 and junctionareas 96 can have a variety of shapes including, but not limited to,circular, oval, square, rectangular, triangular, and the like.

Thereby, the thermoplastic adhesive material 68 provides cavities tohold the superabsorbent polymer particles 66, and thereby immobilizesthis material. In a further aspect, the thermoplastic adhesive material68 bonds to the substrate layer 64 and thus affixes the superabsorbentpolymer particles 66 to the substrate layer 64. In some otherembodiments, the thermoplastic adhesive material 68 will also penetrateat least partly into both the superabsorbent polymer particles 66 andthe substrate layer 64, thus providing for further immobilization andaffixation.

In some other embodiments, the absorbent core 14 may comprise twoabsorbent layers, a first absorbent layer 60 and a second absorbentlayer 62. As best illustrated in FIGS. 5A and 5B, the first absorbentlayer 60 of the absorbent core 14 comprises a substrate layer 64,superabsorbent polymer particles 66 on the substrate layer 64, and athermoplastic adhesive material 68 on the superabsorbent polymerparticles 66. Although not illustrated, the first absorbent layer 60 mayalso include a cover layer such as the cover layer 70 illustrated inFIG. 4.

Likewise, as best illustrated in FIGS. 5A and 5B, the second absorbentlayer 62 of the absorbent core 14 may also include a substrate layer 72,superabsorbent polymer particles 74 on the second substrate layer 72,and a thermoplastic adhesive material 76 on the superabsorbent polymerparticles 74. Although not illustrated, the second absorbent layer 62may also include a cover layer such as the cover layer 70 illustrated inFIG. 4. As mentioned above, the substrate layer 64 of the firstabsorbent layer 60 may be referred to as a dusting layer and has a firstsurface 78 which faces the backsheet 20 of the diaper 10 and a secondsurface 80 which faces the superabsorbent polymer particles 66.Likewise, the substrate layer 72 of the second absorbent layer 62 may bereferred to as a core cover and has a first surface 82 facing thetopsheet 18 of the diaper 10 and a second surface 84 facing thesuperabsorbent polymer particles 74. The first and second substratelayers 64 and 72 may be adhered to one another with adhesive about theperiphery to form an envelope about the superabsorbent polymer particles66 and 74 to hold the superabsorbent polymer particles 66 and 74 withinthe absorbent core 14.

The area of the absorbent core 14 which comprises superabsorbent polymerparticles may vary depending on the desired application of the absorbentcore 14 and the particular absorbent article 10 in which it may beincorporated. In some embodiments, however, the superabsorbent polymerparticles area extends substantially entirely across the absorbent core14. In some alternative embodiments, the superabsorbent polymerparticles area extends entirely across the absorbent core 14 in thecrotch portion 34 of the absorbent article 10 while the superabsorbentpolymer particles area does not extend entirely across the absorbentcore 14 in the front and in the back portions of the absorbent article10.

The first and second absorbent layers 60 and 62 may be combined togetherto form the absorbent core 14 such that the layers may be offset suchthat the superabsorbent polymer particles 66 on the substrate layer 64and the superabsorbent polymer particles 74 on the substrate layer 72are substantially continuously distributed across the superabsorbentpolymer particles area, as illustrated in FIGS. 5A and 5B. In someembodiments, superabsorbent polymer particles 66 and 74 aresubstantially continuously distributed across the superabsorbent polymerparticles area despite superabsorbent polymer particles 66 and 74discontinuously distributed across the first and second substrate layers64 and 72 in clusters 90. In some embodiments, the absorbent layers maybe offset such that the land areas 94 of the first absorbent layer 60face the junction areas 96 of the second absorbent layer 62 and the landareas of the second absorbent layer 62 face the junction areas 96 of thefirst absorbent layer 60, as illustrated in FIGS. 5A and 5B. When theland areas 94 and junction areas 96 are appropriately sized andarranged, the resulting combination of superabsorbent polymer particles66 and 74 is a substantially continuous layer of superabsorbent polymerparticles across the superabsorbent polymer particles area of theabsorbent core 14 (i.e. first and second substrate layers 64 and 72 donot form a plurality of pockets, each containing a cluster 90 ofsuperabsorbent polymer particles 66 and 74 therebetween), as shown onFIG. 5A.

The amount of superabsorbent polymer particles may or not vary along thelength of the core, typically the core being profiled in itslongitudinal direction. It has been found that, for most absorbentarticles such as diapers, the liquid discharge occurs predominately inthe front half of the diaper. The front half of the absorbent core 14should therefore comprise most of the absorbent capacity of the core.Thus, according to certain embodiments, the front half of said absorbentcore 14 may comprise more than about 60% of the superabsorbent polymerparticles, or more than about 65%, 70%, 75%, 80%, 85%, or 90% of thesuperabsorbent polymer particles.

Typically the thermoplastic adhesive material may serve to at leastpartially immobilize the superabsorbent polymer particles both in dryand wet state. The thermoplastic adhesive material can be disposedessentially uniformly between the superabsorbent polymer particles.However, typically the thermoplastic adhesive material may be providedas a fibrous layer which is at least partially in contact with thesuperabsorbent polymer particles and partially in contact with thesubstrate layer(s). Typically, the thermoplastic adhesive material ofthe present invention forms a fibrous network over the superabsorbentpolymer particles. Typically as for example illustrated in FIGS. 5A and5B, the superabsorbent polymer particles 66 and 74 are provided as adiscontinuous layer, and a layer of fibrous thermoplastic adhesivematerial 68 and 76 is laid down onto the layer of superabsorbent polymerparticles 66 and 74, such that the thermoplastic adhesive material 68and 76 is in direct contact with the superabsorbent polymer particles 66and 74, but also in direct contact with the second surfaces 80 and 84 ofthe substrate layers 64 and 72, where the substrate layers are notcovered by the superabsorbent polymer particles 66 and 74. This impartsan essentially three-dimensional structure to the fibrous layer ofthermoplastic adhesive material 68 and 76, which in itself isessentially a two-dimensional structure of relatively small thickness,as compared to the dimension in length and width directions. In otherwords, the thermoplastic adhesive material 68 and 76 undulates betweenthe superabsorbent polymer particles 68 and 76 and the second surfacesof the substrate layers 64 and 72.

The thermoplastic adhesive material may provide cavities to enlace thesuperabsorbent polymer particles, and thereby immobilizes theseparticles. In a further aspect, the thermoplastic adhesive materialbonds to the substrate layer(s) and thus affixes the superabsorbentpolymer particles to the substrate layer(s). Some thermoplastic adhesivematerials will also penetrate into both the superabsorbent polymerparticles and the substrate layer(s), thus providing for furtherimmobilization and affixation. Of course, while the thermoplasticadhesive materials disclosed herein provide an improved wetimmobilization (i.e., immobilization of absorbent material when thearticle is at least partially loaded), these thermoplastic adhesivematerials may also provide a very good immobilization of absorbentmaterial when the absorbent core is dry. The thermoplastic adhesivematerial may also be referred to as a hot melt adhesive.

Without wishing to be bound by theory, it has been found that thosethermoplastic adhesive materials which are most useful for immobilizingthe superabsorbent polymer particles combine good cohesion and goodadhesion behavior. Good adhesion may promote good contact between thethermoplastic adhesive material and the superabsorbent polymer particlesand the substrate layer(s). Good cohesion reduces the likelihood thatthe adhesive breaks, in particular in response to external forces, andnamely in response to strain. When the absorbent core absorbs liquid,the superabsorbent polymer particles swell and subject the thermoplasticadhesive material to external forces. The thermoplastic adhesivematerial may allow for such swelling, without breaking and withoutimparting too many compressive forces, which would restrain thesuperabsorbent polymer particles from swelling.

The thermoplastic adhesive material may comprise, in its entirety, asingle thermoplastic polymer or a blend of thermoplastic polymers,having a softening point, as determined by the ASTM Method D-36-95 “Ringand Ball”, in the range between 50° C. and 300° C., or alternatively thethermoplastic adhesive material may be a hot melt adhesive comprising atleast one thermoplastic polymer in combination with other thermoplasticdiluents such as tackifying resins, plasticizers and additives such asantioxidants. In some embodiments, the thermoplastic polymer hastypically a molecular weight (Mw) of more than 10,000 and a glasstransition temperature (Tg) usually below room temperature or −6°C.<Tg<16° C. In some embodiments, typical concentrations of the polymerin a hot melt are in the range of about 20 to about 40% by weight. Insome embodiments, thermoplastic polymers may be water insensitive.Exemplary polymers are (styrenic) block copolymers including A-B-Atriblock structures, A-B diblock structures and (A-B)n radial blockcopolymer structures wherein the A blocks are non-elastomeric polymerblocks, typically comprising polystyrene, and the B blocks areunsaturated conjugated diene or (partly) hydrogenated versions of such.The B block is typically isoprene, butadiene, ethylene/butylene(hydrogenated butadiene), ethylene/propylene (hydrogenated isoprene), ora mixture thereof.

Other suitable thermoplastic polymers that may be employed aremetallocene polyolefins, which are ethylene polymers prepared usingsingle-site or metallocene catalysts. Therein, at least one comonomercan be polymerized with ethylene to make a copolymer, terpolymer orhigher order polymer. Also applicable are amorphous polyolefins oramorphous polyalphaolefins (APAO) which are homopolymers, copolymers orterpolymers of C2 to C8 alpha olefins.

In some embodiments, the thermoplastic adhesive material is present inthe form of fibers. In some of these embodiments, the fibers will havean average thickness of about 1 to about 50 micrometers or about 1 toabout 35 micrometers and an average length of about 5 mm to about 50 mmor about 5 mm to about 30 mm. To improve the adhesion of thethermoplastic adhesive material to the substrate layer(s) or to anyother layer, in particular any other non-woven layer, such layers may bepre-treated with an auxiliary adhesive.

In certain embodiments the thermoplastic adhesive material is applied onthe substrate layer at an amount of between 0.5 and 30 g/m2, between 1to 15 g/m2, between 1 and 10 g/m2 or even between 1.5 and 5 g/m2 persubstrate layer.

An exemplary thermoplastic adhesive material 68 and 76 may have astorage modulus G′ measured at 20° C. of at least 30,000 Pa and lessthan 300,000 Pa, or less than 200,000 Pa, or between 140,000 Pa and200,000 Pa, or less than 100,000 Pa. In a further aspect, the storagemodulus G′ measured at 35° C. may be greater than 80,000 Pa. In afurther aspect, the storage modulus G′ measured at 60° C. may be lessthan 300,000 Pa and more than 18,000 Pa, or more than 24,000 Pa, or morethan 30,000 Pa, or more than 90,000 Pa. In a further aspect, the storagemodulus G′ measured at 90° C. may be less than 200,000 Pa and more than10,000 Pa, or more than 20,000 Pa, or more then 30,000 Pa. The storagemodulus measured at 60° C. and 90° C. may be a measure for the formstability of the thermoplastic adhesive material at elevated ambienttemperatures. This value is particularly important if the absorbentproduct is used in a hot climate where the thermoplastic adhesivematerial would lose its integrity if the storage modulus G′ at 60° C.and 90° C. is not sufficiently high.

G′ is measured using a rheometer as schematically illustrated in FIG. 6for the purpose of general illustration only. The rheometer 627 iscapable of applying a shear stress to the adhesive and measuring theresulting strain (shear deformation) response at constant temperature.The adhesive is placed between a Peltier-element acting as lower, fixedplate 628 and an upper plate 629 with a radius R of 10 mm, which isconnected to the drive shaft of a motor to generate the shear stress.The gap between both plates has a height H of 1500 micron. ThePeltier-element enables temperature control of the material (+0.5° C.).The strain amplitude is set at 0.05%, the strain frequency at 1 Hz andthe cooling rate at 2° C./min (with start temperature at 150° C. orhigher and end temperature at −5° C.).

The absorbent core may also comprise an auxiliary adhesive which is notillustrated in the figures. The auxiliary adhesive may be deposited onthe substrate layer(s) before application of the superabsorbent polymerparticles on the substrate layer(s) for enhancing adhesion of thesuperabsorbent polymer particles and the thermoplastic adhesive materialto the respective substrate layer. The auxiliary adhesive may also aidin immobilizing the superabsorbent polymer particles and may comprisethe same thermoplastic adhesive material as described hereinabove or mayalso comprise other adhesives including but not limited to sprayable hotmelt adhesives. An example of commercially available auxiliary adhesiveis H.B. Fuller Co. (St. Paul, Minn.) Product No. HL-1620-B. Theauxiliary adhesive may be applied to the substrate layer(s) by anysuitable means, but according to some embodiments, may be applied inabout 0.5 to about 1 mm wide slots spaced about 0.5 to about 2 mm apart.

The Topsheet

The absorbent article 10 may comprise a topsheet 18 which may be liquidpervious. The topsheet 18 may be manufactured from a wide range ofmaterials such as woven and nonwoven materials; polymeric materials suchas apertured formed thermoplastic films, apertured plastic films, andhydroformed thermoplastic films; porous foams; reticulated foams;reticulated thermoplastic films; and thermoplastic scrims. Suitablewoven and nonwoven materials can be included of natural fibers (e.g.,wood or cotton fibers), synthetic fibers (e.g., polymeric fibers such aspolyester, polypropylene, or polyethylene fibers) or from a combinationof natural and synthetic fibers.

In some embodiments, the topsheet 18 may be made of a hydrophobicmaterial to isolate the wearer's skin from liquids which have passedthrough the topsheet 18. In such embodiments, at least a part of theupper surface of the topsheet 18 is treated to be hydrophilic so thatliquids will transfer through the topsheet 18 more rapidly. Thisdiminishes the likelihood that body exudates will flow off the topsheet18 rather than being drawn through the topsheet 18 and being absorbed bythe absorbent core. The topsheet 18 can be rendered hydrophilic bytreating it with a surfactant. Suitable methods for treating thetopsheet 18 with a surfactant include spraying the topsheet materialwith the surfactant and immersing the material into the surfactant.

In some embodiments, the topsheet includes an apertured formed film.Apertured formed films are are pervious to body exudates and yetnon-absorbent and have a reduced tendency to allow liquids to pass backthrough and rewet the wearer's skin. Thus, the surface of the formedfilm which is in contact with the body remains dry, thereby reducingbody soiling and creating a more comfortable feel for the wearer.Suitable formed films are described in U.S. Pat. No. 3,929,135, entitled“Absorptive Structures Having Tapered Capillaries”, issued to Thompsonon Dec. 30, 1975; U.S. Pat. No. 4,324,246 entitled “Disposable AbsorbentArticle Having A Stain Resistant Topsheet”, issued to Mullane, et al. onApr. 13, 1982; U.S. Pat. No. 4,342,314 entitled “Resilient Plastic WebExhibiting Fiber-Like Properties”, issued to Radel, et al. on Aug. 3,1982; U.S. Pat. No. 4,463,045 entitled “Macroscopically ExpandedThree-Dimensional Plastic Web Exhibiting Non-Glossy Visible Surface andCloth-Like Tactile Impression”, issued to Ahr, et al. on Jul. 31, 1984;and U.S. Pat. No. 5,006,394 “Multilayer Polymeric Film” issued to Bairdon Apr. 9, 1991.

Alternatively, the topsheet includes apertured nonwoven materials.Suitable apertured nonwoven materials are described in U.S. Pat. No.5,342,338 and in PCT Application No. WO 93/19715.

The Backsheet

The absorbent article may comprise a backsheet 20 which may be attachedto the topsheet. The backsheet may prevent the exudates absorbed by theabsorbent core and contained within the diaper from soiling otherexternal articles that may contact the diaper, such as bed sheets andundergarments. In some embodiments, the backsheet may be substantiallyimpervious to liquids (e.g., urine) and comprise a laminate of anonwoven and a thin plastic film such as a thermoplastic film having athickness of about 0.012 mm (0.5 mil) to about 0.051 mm (2.0 mils).Suitable backsheet films include those manufactured by TredegarIndustries Inc. of Terre Haute, Ind. and sold under the trade namesX15306, X10962, and X10964. Other suitable backsheet materials mayinclude breathable materials that permit vapors to escape from thediaper while still preventing liquid exudates from passing through thebacksheet. Exemplary breathable materials may include materials such aswoven webs, nonwoven webs, composite materials such as film-coatednonwoven webs, and microporous films such as manufactured by MitsuiToatsu Co., of Japan under the designation ESPOIR NO and by EXXONChemical Co., of Bay City, Tex., under the designation EXXAIRE. Suitablebreathable composite materials comprising polymer blends are availablefrom Clopay Corporation, Cincinnati, Ohio under the name HYTREL blendP18-3097. Such breathable composite materials are described in greaterdetail in PCT Application No. WO 95/16746, published on Jun. 22, 1995 inthe name of E.I. DuPont. Other breathable backsheets including nonwovenwebs and apertured formed films are described in U.S. Pat. No. 5,571,096issued to Dobrin et al. on Nov. 5, 1996.

Test Methods

-   -   K(t) Test Method (Dynamic Effective Permeability and Uptake        Kinetics Measurement Test method)

This method determines the time dependent effective permeability (K(t))and the uptake kinetics of an absorbent structure containingsuperabsorbent polymer particles under a confining pressure. Theobjective of this method is to assess the ability of the absorbentstructure containing superabsorbent polymer particles to acquire anddistribute body fluids when the polymer is present at highconcentrations in an absorbent article and exposed to mechanicalpressures as they typically occur during use of the absorbent article.Darcy's law and steady-state flow methods are used to calculateeffective permeability (see below). (See also for example, “Absorbency,”ed. by P. K. Chatterjee, Elsevier, 1982, Pages 42-43 and “ChemicalEngineering Vol. II, Third Edition, J. M. Coulson and J. F. Richardson,Pergamon Press, 1978, Pages 122-127.)

In contrast to previously published methods, the sample is notpreswollen therefore the hydrogel is not formed by preswellinghydrogel-forming superabsorbent polymer particles in synthetic urine,but the measurement is started with a dry structure.

The equipment used for this method is called ‘ZeitabhängigerDurchlässigkeitsprüfstand’ or ‘Time Dependent Permeability Tester’,Equipment No. 03-080578 and is commercially available at BRAUN GmbH,Frankfurter Str. 145, 61476 Kronberg, Germany and is described below.Upon request, operating instructions, wiring diagrams and detailedtechnical drawings are also available.

Dynamic Effective Permeability and Uptake Kinetic Measurement System

FIG. 7 shows the dynamic effective permeability and uptake kineticmeasurement system, called ‘Time Dependent Permeability Tester’ herein.

The equipment consists of the following main parts:

-   -   M11 Digital Laser Sensor for caliper measurement 701 (MEL        Mikroelektronik GmbH, 85386 Eching, Germany    -   Fiber for Liquid Level Detection 702 (FU95, Keyence Corp.,        Japan)    -   Digital Fiber Sensor 703 (FS-N10, Keyence Corp., Japan)    -   Precision Balance 704 (XP6002MDR, Mettler Toledo AG, 8606        Greifensee, Switzerland)    -   Power Unit Logo!Power (C98130-A7560-A1-5-7519, Siemens AG)    -   Labview Software License 706 (National Instruments, Austin, Tx,        USA)    -   Receiving Vessel 707 (5 L Glass Beaker, Roth)    -   Reservoir 708 (5 L Glass bottle, VWR) with joint 709 and        open-end tube for air admittance 723    -   Operating unit and console 705 (Conrad Electronics)    -   Computerized data acquisition system 710    -   A piston/cylinder assembly 713 as described herein    -   A controlled valve 714 (Bürkert)

FIG. 8 shows the piston/cylinder assembly 713 comprising piston guidinglid 801, piston 802 and cylinder 803. The cylinder 803 is made oftransparent polycarbonate (e.g., Lexan®) and has an inner diameter p of6.00 cm (area=28.27 cm²). The inner cylinder walls 850 are smooth; theheight of the cylinder r is about 7.50 cm. The bottom 804 of thecylinder 803 is faced with a US. Standard 400 mesh stainless-steelscreen cloth (not shown) (e.g. from Weisse and Eschrich) that isbi-axially stretched to tautness prior to attachment to the bottom 804of the cylinder 803. The piston 802 is composed of a stainless steelpiston body 805 and a stainless steel head 806. The piston head 806diameter q is slightly less than 6 cm so as to slide freely into thecylinder 803 without leaving any gap for the hydrogel-forming particleto pass trough. The piston body 805 is firmly attached perpendicularlyat the center of the piston head 806. The piston body diameter t isabout 2.2 cm. The piston body 805 is then inserted into a piston guidinglid 801. The guiding lid 801 has a POM (Polyoxymethylene) ring 809 witha diameter allowing a free sliding of the piston 802 yet keeping thepiston body 805 perfectly vertical and parallel to the cylinder walls850 once the piston 802 with the guiding lid 801 are positioned on topof the cylinder 803. The top view of the piston head 806 is shown inFIG. 9. The piston head 806 is meant to apply the pressure homogeneouslyto the sample 718. It is also highly permeable to the hydrophilic liquidso as to not limit the liquid flow during measurement. The piston head806 is composed of a US. standard 400 mesh stainless steel screen cloth903 (e.g. from Weisse and Eschrich) that is bi-axially stretched totautness and secured at the piston head stainless steel outer ring 901.The entire bottom surface of the piston is flat. Structural integrityand resistance to bending of the mesh screen is then ensured by thestainless steel radial spokes 902. The height of the piston body 805 isselected such that the weight of the piston 802 composed of the pistonbody 805 and the piston head 806 is 596 g (±6 g), this corresponds to0.30 psi over the area of the cylinder 803.

The piston guiding lid 801 is a flat circle of stainless steel with adiameter s of about 7.5 cm held perpendicular to the piston body 805 bythe POM ring 809 in its center. There are two inlets in the guiding lid(810 and 812).

The first inlet 812, allows the Fiber for Liquid Level Detection 702 tobe positioned exactly 5 cm above the top surface of the screen (notshown) attached to the bottom (804) of the cylinder 803 once the piston802 is assembled with the cylinder 803 for the measurement.

The second inlet 810 allows connecting a liquid tube 721 providing theliquid to the experiment.

To make sure that the assembly of the piston 802 with the cylinder 803is done consistently a slit 814 is made on the cylinder 803 matching aposition marker 813 in the guiding lid 801. In this way the rotationangle of the cylinder and the guiding lid is always the same.

Prior to every use, the stainless steel screen cloth 903 of the pistonhead 806 and cylinder 803 should be inspected for clogging, holes orover-stretching and replaced when necessary. A K(t) apparatus withdamaged screen can deliver erroneous K(t) and uptake kinetic results,and must not be used until the screen has been replaced.

A 5 cm mark 808 is scribed on the cylinder at a height k of 5.00 cm(±0.02 cm) above the top surface of the screen attached to the bottom804 of the cylinder 803. This marks the fluid level to be maintainedduring the analysis. The Fiber for Liquid Level Detection 702 ispositioned exactly at the 5 cm mark 808. Maintenance of correct andconstant fluid level (hydrostatic pressure) is critical for measurementaccuracy

A reservoir 708 connected via tubing to the piston/cylinder assembly 713holding the sample and a controller valve 714 are used to deliver saltsolution to the cylinder 803 and to maintain the level of salt solutionat a height k of 5.00 cm above the top surface of screen attached to thebottom of the cylinder 804. The valve 714, the Fiber for Liquid LevelDetection 702 and the Digital Fiber Sensor 703 are connected to thecomputerized acquisition system 710 trough the operating unit 705. Thisallows the Dynamic Effective Permeability and Uptake Kinetic MeasurementSystem to use the information from the Fiber for Liquid Level Detection702 and the Digital Fiber Sensor 703 to control the valve 714 andultimately maintain the level of the liquid at the 5 cm mark 808.

The reservoir 708 is placed above the piston/cylinder assembly 713 insuch a manner as to allow a 5 cm hydrohead to be formed within 15seconds of initiating the test, and to be maintained in the cylinderthroughout the test procedure. The piston/cylinder assembly 713 ispositioned on the support ring 717 of the cover plate 716 and the firstinlet 812 is held in place with the docking support 719. This allowsonly one position of the guiding lid 801. Furthermore, due to theposition marker 813, there is also only one position for the cylinder803. The screen attached to the bottom of the cylinder 804 must beperfectly level and horizontal. The supporting ring 717 needs to have aninternal diameter small enough, so to firmly support cylinder 803 butlarger than 6.0 cm so to lay outside of the internal diameter of thecylinder once the cylinder is positioned on the supporting ring 717.This is important so to avoid any interference of the supporting ring717 with the liquid flow.

The salt solution, applied to the sample 718 with a constant hydroheadof 5 cm can now freely flow from the piston/cylinder assembly 713 into areceiving vessel 707 positioned on the balance 704 which is accuratewithin ±0.01 g. The digital output of the balance is connected to acomputerized data acquisition system.

The caliper (thickness) of the sample is constantly measured with aDigital Laser Sensor for caliper measurement 701. The laser beam 720 ofthe digital laser sensor 701 is directed at the center of the POM coverplate 811 of the piston body. The accurate positioning of all the partsof the piston/cylinder assembly 713 allows the piston body 805 to beperfectly parallel to the laser beam 720 and as a result an accuratemeasure of the thickness is obtained.

Test Preparation

The reservoir 708 is filled with test solution. The test solution is anaqueous solution containing 9.00 grams of sodium chloride and 1.00 gramsof surfactant per liter of solution. The preparation of the testsolution is described below. The receiving vessel 707 is placed on thebalance 704 which is connected to a computerized data acquisition system710. Before the start of the measurement the balance is reset to zero.

Preparation of Test Liquid: Chemicals Needed:

-   -   Sodium Chloride (CAS#7647-14-5, eg: Merck, cat#1.06404.1000)    -   Linear C₁₂-C₁₄ alcohol ethoxylate (CAS#68439-50-9, eg. Lorodac®,        Sasol, Italy)    -   Deionized H₂O

Ten liters of a solution containing 9.00 grams per litre of NaCl and1.00 grams per liter linear C12-C14 alcohol ethoxalate in distilledwater is prepared and equilibrated at 23° C.±1° C. for 1 hour. Thesurface tension is measured on 3 individual aliquots and should be28±0.5 mN/m. If the surface tension of the solution is different from28±0.5 mN/m, the solution is discarded and a new test solution isprepared. The test solution has to be used within 36 hours from itspreparation and is considered expired afterwards.

K(t) Sample Preparation

A representative, circular portion of the absorbent structure of 6.00 cmdiameter is obtained. The portion of the absorbent article can beobtained with a suitable circular die and a hydraulic press cutter (likee.g. Electro-Hydraulic Alfa Cutter 240-10 available at Thwing-Albertinstrument company, 14 W. Collings Ave. West Berlin, N.J. 08091).

The circular sample 118 is carefully positioned flat on the screen (notshown) attached to the bottom 204 of the cylinder 203 occupying all theavailable surface on the screen. It is important to position thecircular sample 118 in a way that the side in direct contact with thescreen is the one that in use is usually more distant from the liquidsource so as to reproduce the common flow direction in use. For examplefor samples related to absorbent articles such as diapers, the sideusually facing the wearer should be positioned on top while the sidefacing the garments should be positioned in contact with the screen atthe bottom of the cylinder. A careful positioning of the sample iscritical for the measurement's accuracy. In case the dimension of theabsorbent structure is small and a 6.0 cm diameter sample cannot beobtained from it, it is possible to join two absorbent structures ofequal size so to obtain the minimum sample size necessary. The twosamples need to be taken in the same position from two identicalabsorbent structures. The two absorbent structures should be joinedthrough a straight edge and if necessary cut to obtain such a straightedge. The intent is that the joined edges recreate a flat homogeneouslayer with no or only a minimal gap. This joint layer is then handledaccording to the standard sample preparation described above with theadditional precaution to center the join line in the cutting die so toobtain two half circles of identical shape. It is important that boththe half circles are carefully positioned inside the sample holder so torecreate a full circle and occupying the entire available surface on thescreen with no or only a minimal gap. Both the halves have to bepositioned with the side facing the screen as explained above. However,in most embodiments, the sample will consist of a unitary circularportion of the absorbent structure.

Method for Extracting an Absorbent Structure from an Absorbent Article

The absorbent article is positioned on a flat surface. In case theproduct contains features that prevent it to lay flat (such as the cuffelastics) they are cut at suitable intervals to allow the product to layflat.

Portion(s) of the absorbent structure comprising at least 90% by weightof superabsorbent polymer particles to be tested according to the K(t)Test Method are first identified and should be isolated as explainedhereinbelow.

All materials which are not part of the absorbent structure are removedfrom the absorbent structure paying attention to not unduly damage theabsorbent structure.

If the materials to be removed are attached to the absorbent structurefor example by adhesive material such as thermoplastic adhesivematerial, to avoid damages to the structure, they could be removed withthe aid of Cold sprays with a cooling temperature from −50 to −60° C.(such as “IT Icer” or “PRF 101 cold spray” available at Taerosol,Kangasala Finland) as shown for example in FIG. 15.

FIG. 15 shows an absorbent structure 151 comprising superabsorbentpolymer polymer particles 152 which are sandwiched between two substratelayers 153, 154. A layer of material 156 is attached to one of thesubstrate layers 153, 154 and is therefore not part of the absorbentstructure 151. This layer needs to be removed from the absorbentstructure 151. To avoid undue damage to the absorbent structure 151 thelayer of material 156 to be removed from the absorbent structure 151 ispulled off the absorbent structure 151 in a 180° peel geometry while theadhesive material 155 is cooled with the Cold spray 157. The sprayingshould last at least 1 seconds but no more than 5 seconds for eachsingle portion of the layer of material 156.

After removal of each material, the remaining part of the absorbentstructure is kept under 0.3 psi pressure until the temperature is backto the initial value (TAPPI lab condition).

The upper layer and/or the lower layer of the absorbent structure may beproperly perforated to allow liquid flow through as shown for example inFIG. 16 representing an absorbent structure 161 comprisingsuperabsorbent polymer particles 162 which are sandwiched between twosubstrate layers 163, 164. The perforation is performed using a hotmetal tip also called perforating tip 165 which comprises a steel rod166 with a diameter H of 0.7±0.2 mm. A standard paper clip, bend arounda solder tip 167 such as CT 60/621 available at ERSA GmbH, Wertheim,Germany can be used for the purpose. The perforating tip 165 should beset at the temperature of 310±20° C. The perforating tip 165 ispositioned in contact with the layers to be perforated for a shortperiod of time with low pressure so to perforate the layers, for exampleby melting without affecting any of the other materials of the absorbentstructure 161. The holes are created with the same procedure in aregular square perforation pattern with a hole edge to edge distance Dof 1±0.2 mm, as shown for example in FIG. 17.

Each absorbent structure is visually checked for integrity and discardedif damaged with the help of a back light. Examples of damages are forexamples: cuts, holes, wrinkles which were not present before removingthe absorbent structure from the absorbent article. The perforations inthe layers done with the perforating tip, are not considered damagesunless they affect other layers. The substantial migration ofsuperabsorbent polymer particles and fibers within the absorbentstructure is also considered damage.

The absorbent structures prepared as such are then cut according theK(t) test method

K(t) Procedure

The measurement is carried out at Tappi lab conditions: 23° C.±1° C./50%RH±2%.

The empty piston/cylinder assembly 713 is mounted in the circularopening in the cover plate 716 and is supported around its lowerperimeter by the supporting ring 717. The piston/cylinder assembly 713is held in place with the docking support 719 with the cylinder 803 andpiston 802 aligned at the proper angle. The reference caliper reading(r_(r)) is measured by Digital Laser sensor. After this, the emptypiston/cylinder assembly 713 is removed from the cover plate 716 andsupporting ring 717 and the piston 802 is removed from the cylinder 803.

The sample 718 is positioned (absorbent structure) on the cylinderscreen as explained above. After this, the piston 802 assembled with theguiding lid 801 is carefully set into the cylinder 803 by matching theposition marker 813 of the guiding lid 801 with the slit 814 made in thecylinder 803

The piston/cylinder assembly is held in place with the docking support719 with the cylinder and piston aligned at the proper angle

This can be only done in one way. The liquid tube 721 connected to thereservoir 708 and the Digital Fiber Sensor 703 are inserted into thepiston/cylinder assembly 713 via the two inlets 810 and 812 in theguiding lid 801.

The computerized data acquisition system 710 is connected to the balance704 and to the digital laser sensor for caliper measurement 701. Fluidflow from the reservoir 708 to the cylinder 803 is initiated by thecomputer program by opening valve 714. The cylinder is filled until the5 cm mark 808 is reached in 5 to 15 seconds, after which the computerprogram regulates the flow rate to maintain a constant 5 cm hydrohead.The quantity of solution passing through the sample 718 is measured bythe balance 704 and the caliper increase is measured by the lasercaliper gauge. Data acquisition is started when the fluid flow isinitiated specifically when the valve 714 is opened for the first time,and continues for 21 minutes or until the reservoir runs dry so that the5 cm hyrdrohead is no longer maintained. The duration of one measurementis 21 min, laser caliper and balance readings are recorded regularlywith an interval that may vary according to the measurement scope from 2to 10 sec, and 3 replicates are measured.

After 21 min, the measurement of the 1^(st) replicate is successfullycompleted and the controlled valve 714 closes automatically. Thepiston/cylinder assembly 713 is removed and the measurements of the2^(nd) and 3^(rd) replicates are done accordingly, always following thesame procedure. At the end of the measurement of the 3^(rd) replicate,the controlled valve 714 stops the flow of liquid and stopcock 722 ofthe reservoir 708 is closed. The collected raw data is stored in theform of a simple data table, which then can be imported easily to aprogram for further analysis e.g. Excel 2003, SP3.

In the data table the following relevant information is reported foreach reading:

-   -   Time from the beginning of the experiment    -   Weight of the liquid collected by the receiving vessel 707 on        the balance 704    -   Caliper of the sample 718

The data from 30 seconds to the end of the experiment are used in theK(t) and uptake kinetics calculation. The data collected in the first 30seconds are not included in the calculation. The effective permeabilityK(t) and the uptake kinetics of the absorbent structure are thendetermined using the equation sets below.

Used Equations:

The table below describes the notation used in the equations.

A x-section of the absorbent structure sample which corresponds to thecylinder inner radius: 28.27 cm² h height of water column, 5.0 cm Δpdriving pressure applied by the 5.00 cm hydrohead (h): 4929.31 g/(cm s²)G gravity constant: 981 cm/s² η Temperature dependent effectiveviscosity of the liquid in g/(cm s) T Temperature in ° C. ρ density ofthe liquid: 1.0053 g/cm³ ρ_(s) ^(A) Apparent sample density of theporous medium or powder in g/cm³ ρ_(s) Average density of the solid partof the dry sample in g/cm³ ρ_(s k) Density of the component k of the drysample in g/cm³ M dry mass of the sample in g: 2.00 g if measuringsuperabsorbent particles m_(k) Mass of the component k of the dry samplein g V_(s) Dry sample volume in cm³ t_(i) time at step i of N discretepoints in s d_(i) caliper of the absorbent structure sample at timet_(i) in cm r_(i) reading of caliper instrument at time t_(i) in cmr_(r) reference reading of caliper instrument (reading of thepiston/cylinder assembly without sample) in cm m_(out i) balance readingat time t_(i); mass of the liquid that left the sample at time t_(i) ing U(t_(i)) Sample uptake at time t_(i) in g T20 time required to reachan uptake of 20 g/g, starting at 0 s (t₀) in s U20 Sample uptake after20 minutes in g/g T80% Time required to reach an uptake of 80% of U20starting at 0 s (t₀) in s K20 Sample permeability at 20 minutes in m²Kmin the minimum value of the permeability during the experiment in m²Kmin/K20 the ratio of Kmin and K20

The driving pressure is calculated from the hydro head as follows:

Δp=h·G·ρ=4929.31 g/(cm·s²)

The caliper at each time t_(i) is calculated as the difference of thecaliper sensor reading at time t_(i) and the reference reading withoutsample:

d _(i) =r _(i) −r _(r) [cm]

For superabsorbent particles samples the caliper of the sample at timet₁=0 (d₀) is used to evaluate the quality of the particle sprinkling

An apparent sample density inside the cylinder can be in fact calculatedas:

$\rho_{s}^{A} = {\frac{m}{d_{0} \cdot A}\mspace{14mu}\left\lbrack {g\text{/}{cm}^{3}} \right\rbrack}$

If this apparent density inside the cylinder differs from the apparentdensity of the powder by more than ±40% the measurement has to beconsidered invalid and eliminated.

The apparent density can be measured according EDANA method 406.2-02(“Superabsorbent materials—Polyacrylate superabsorbentpowders—GRAVIMETRIC DETERMINATION OF DENSITY”)

The rate of change with time of the balance reading at time t_(i) iscalculated as follows:

$\frac{{m_{out}\left( t_{i} \right)}}{t} = {\frac{m_{{out}_{i + 1}} - m_{{out}_{i - 1}}}{t_{i + 1} - t_{i - 1}}\mspace{14mu}\left\lbrack {g\text{/}\sec} \right\rbrack}$

The rate of change with time of the caliper reading at time t_(i) iscalculated as follows:

$\frac{{d\left( t_{i} \right)}}{t} = {\frac{d_{i + 1} - d_{i - 1}}{t_{i + 1} - t_{i - 1}}\mspace{14mu}\left\lbrack {{cm}\text{/}\sec} \right\rbrack}$

The uptake Kinetics is calculated as follows:

${U\left( t_{i} \right)} = {\frac{\left( {{A \cdot d_{i}} - V_{s}} \right) \cdot \rho}{m}\mspace{14mu}\left\lbrack {g\text{/}g} \right\rbrack}$

By dry sample volume (V_(s)) is intended the skeletal volume of thesample therefore V_(s) is the actual volume occupied by the solidmaterial in the dry sample excluding pores and interstitials that mightbe present.

V_(s) can be calculated or measured by different methods known by theskilled person for example, knowing the exact composition and theskeletal density of the components it can be determined as follows:

${Vs} = {{\sum\limits_{k}\; V_{k}} = {\sum\limits_{k}\; {\frac{m_{k}}{\rho_{sk}}\mspace{14mu}\left\lbrack {cm}^{3} \right\rbrack}}}$

Alternatively for an unknown material composition V_(s) can be easilycalculated as follow:

$V_{S} = {\frac{m}{\rho_{s}}\mspace{14mu}\left\lbrack {cm}^{3} \right\rbrack}$

The average density ρ_(s) can be determined by pycnometry with asuitable non-swelling liquid of known density. This technique cannot beperformed on the same samples subsequently used for the K(t) measuretherefore a suitable additional representative set of samples should beprepared for this experiment measurement.

From U(t) at the different time steps calculated as explained above, onecan determine the uptake at any specific time by linear interpolation.For example one of the important outputs is the uptake at 20 minutesalso called U20 (in g/g).

From U(t) at the different time steps one can also determine the timerequired to reach a certain uptake by linear interpolation. The timewhere the uptake of 20 g/g is first reached is called T20. Similarly thetime to reach any other uptakes can be calculated accordingly (e,g T5 orT10). Knowing U20 it is possible to determine from U(t) at the differenttime steps also the time to reach 80% of U20, this property is calledT80%.

The Effective Permeability is calculated as follows from the rates ofmass change and caliper change:

${K\left( t_{i} \right)} = {\eta {\frac{d_{i}}{\Delta \; p} \cdot {\left( {{\frac{1}{\rho \cdot A} \cdot \frac{{m_{out}\left( t_{i} \right)}}{t}} + \frac{{d\left( t_{i} \right)}}{t}} \right)\mspace{14mu}\left\lbrack {cm}^{2} \right\rbrack}}}$

The effective viscosity of the liquid depends on the temperature and inthe interval of the experiment (23° C.±1° C.) is calculated accordingthe following empirical equation:

η=A+B·T [g/(cm·s)]

-   -   wherein A=1,479.10⁻² [g/(cm·s)] and B=−2.36.10⁻⁴ [g/(cm·s.° C.)]

From K(t_(i)) one can determine the effective permeability at a certaintime by linear interpolation. For example one of the important outputsis the uptake at 20 minutes or K20 (m²). Similarly the Permeability atany other time can be calculated accordingly (e.g. K5 or K10).

Another parameter to be derived from the data is Kmin, which is theminimum K(t) value measured over the whole curve in the interval fromt_(i)=30 s to t_(i)=1200 s. This value is useful to calculate Kmin/K20which is the ratio between the minimum effective permeability and thepermeability at 20 minutes. This parameter express the temporary gelblocking that might occur in some of the samples. If the value is closeto 1 there is no temporary gel blocking if the value is close to 0 it isan indication that the material goes through a strong effectivepermeability drop when initially loaded with liquid.

The average values for T20, T80%, K20, U20 and Kmin/K20 are reportedfrom 3 replicates according to the accuracy required as known by theskilled man.

Caliper Measurement Test Method,

The intent of this method is to provide a procedure to determine thethickness of the absorbent core at the crotch point of an absorbentarticle. The test can be executed with a conventional caliper gauge,such as Type EG-225 available from ONO SOKKI Technology Inc., 2171Executive Drive, Suite 400, Addison, Ill. 60101, USA, with anappropriate gauge stand, having an aluminium circular sample foot of 41mm diameter, having a force exerted by the foot of 10 gf. An additionalweight is added to achieve a total of 160 gf to adjust the pressure to1.18 kPa (0.173 psi).

The thickness of the absorbent core is determined prior to assembly ofthe absorbent core in the absorbent article after the exact positionwhich the absorbent core will have in the absorbent article uponassembly has been decided on. However, the thickness may also bedetermined after removing of the absorbent core from a finished productby any suitable method known by the person skilled in the art.

The crotch point of an absorbent article is determined at theintersection of the longitudinal centerline and the transversecenterline of the article.

Basic Protocol

-   -   1. All testing is conducted at 23±1° C. and 50±2% relative        humidity.    -   2. The absorbent core is allowed to equilibrate at 23±1° C. and        50±2% relative humidity for 8 hours.    -   3. The crotch point is determined as described above and marked        on the wearer surface of the absorbent core.    -   4. The absorbent core is positioned under the caliper gauge with        the wearer surface toward the sample contact foot and with the        crotch point centered under the foot.    -   5. The sample contact foot is gently lowered into contact with        the surface of the absorbent core.    -   6. The caliper reading is taken 5 seconds after the foot comes        into contact with the absorbent core.

Urine Permeability Measurement (UPM) Test method

Urine Permeability Measurement System

This method determined the permeability of a swollen hydrogel layer1318. The equipment used for this method is described below. This methodis closely related to the SFC (Saline Flow Conductivity) test method ofthe prior art.

FIG. 10 shows permeability measurement system 1000 set-up with theconstant hydrostatic head reservoir 1014, open-ended tube for airadmittance 1010, stoppered vent for refilling 1012, laboratory jack1016, delivery tube 1018, stopcock 1020, ring stand support 1022,receiving vessel 1024, balance 1026 and piston/cylinder assembly 1028.

FIG. 11 shows the piston/cylinder assembly 1028 comprising a metalweight 1112, piston shaft 1114, piston head 1118, lid 1116, and cylinder1120. The cylinder 1120 is made of transparent polycarbonate (e.g.,Lexan®) and has an inner diameter p of 6.00 cm (area=28.27 cm²) withinner cylinder walls 1150 which are smooth. The bottom 1148 of thecylinder 1120 is faced with a US. Standard 400 mesh stainless-steelscreen cloth (not shown) that is bi-axially stretched to tautness priorto attachment to the bottom 1148 of the cylinder 1120. The piston shaft1114 is made of transparent polycarbonate (e.g., Lexan®) and has anoverall length q of approximately 127 mm. A middle portion 1126 of thepiston shaft 1114 has a diameter r of 21.15 mm. An upper portion 1128 ofthe piston shaft 1114 has a diameter s of 15.8 mm, forming a shoulder1124. A lower portion 1146 of the piston shaft 1114 has a diameter t ofapproximately ⅝ inch and is threaded to screw firmly into the centerhole 1218 (see FIG. 12) of the piston head 1118. The piston head 1118 isperforated, made of transparent polycarbonate (e.g., Lexan®), and isalso screened with a stretched US. Standard 400 mesh stainless-steelscreen cloth (not shown). The weight 1112 is stainless steel, has acenter bore 1130, slides onto the upper portion 1128 of piston shaft1114 and rests on the shoulder 1124. The combined weight of the pistonhead 1118, piston shaft 1114 and weight 1112 is 596 g (±6 g), whichcorresponds to 0.30 psi over the area of the cylinder 1120. The combinedweight may be adjusted by drilling a blind hole down a central axis 1132of the piston shaft 1114 to remove material and/or provide a cavity toadd weight. The cylinder lid 1116 has a first lid opening 1134 in itscenter for vertically aligning the piston shaft 1114 and a second lidopening 1136 near the edge 1138 for introducing fluid from the constanthydrostatic head reservoir 1014 into the cylinder 1120.

A first linear index mark (not shown) is scribed radially along theupper surface 1152 of the weight 1112, the first linear index mark beingtransverse to the central axis 1132 of the piston shaft 1114. Acorresponding second linear index mark (not shown) is scribed radiallyalong the top surface 1160 of the piston shaft 1114, the second linearindex mark being transverse to the central axis 1132 of the piston shaft1114. A corresponding third linear index mark (not shown) is scribedalong the middle portion 1126 of the piston shaft 1114, the third linearindex mark being parallel with the central axis 1132 of the piston shaft1114. A corresponding fourth linear index mark (not shown) is scribedradially along the upper surface 1140 of the cylinder lid 1116, thefourth linear index mark being transverse to the central axis 1132 ofthe piston shaft 1114. Further, a corresponding fifth linear index mark(not shown) is scribed along a lip 1154 of the cylinder lid 1116, thefifth linear index mark being parallel with the central axis 1132 of thepiston shaft 1114. A corresponding sixth linear index mark (not shown)is scribed along the outer cylinder wall 1142, the sixth linear indexmark being parallel with the central axis 1132 of the piston shaft 1114.Alignment of the first, second, third, fourth, fifth, and sixth linearindex marks allows for the weight 1112, piston shaft 1114, cylinder lid1116, and cylinder 1120 to be re-positioned with the same orientationrelative to one another for each measurement.

The cylinder 1120 specification details are:

-   -   Outer diameter u of the Cylinder 1120: 70.35 mm    -   Inner diameter p of the Cylinder 1120: 60.0 mm    -   Height v of the Cylinder 1120: 60.5 mm

The cylinder lid 1116 specification details are:

-   -   Outer diameter w of cylinder lid 1116: 76.05 mm    -   Inner diameter x of cylinder lid 1116: 70.5 mm    -   Thickness y of cylinder lid 1116 including lip 1154: 12.7 mm    -   Thickness z of cylinder lid 1116 without lip 1154: 6.35 mm    -   Diameter a of first lid opening 1134: 22.25 mm    -   Diameter b of second lid opening 1136: 12.7 mm    -   Distance between centers of first and second lid openings 1134        and 1136: 23.5 mm

The weight 1112 specification details are:

-   -   Outer diameter c: 50.0 mm    -   Diameter d of center bore 1130: 16.0 mm    -   Height e: 39.0 mm

The piston head 1118 specification details are

-   -   Diameter f: 59.7 mm    -   Height g: 16.5 mm    -   Outer holes 1214 (14 total) with a 9.65 mm diameter h, outer        holes 1214 equally spaced with centers being 47.8 mm from the        center of center hole 1218    -   Inner holes 1216 (7 total) with a 9.65 mm diameter i, inner        holes 1216 equally spaced with centers being 26.7 mm from the        center of center hole 1218    -   Center hole 1218 has a diameter j of ⅝ inches and is threaded to        accept a lower portion 1146 of piston shaft 1114.

Prior to use, the stainless steel screens (not shown) of the piston head1118 and cylinder 1120 should be inspected for clogging, holes orover-stretching and replaced when necessary. A urine permeabilitymeasurement apparatus with damaged screen can deliver erroneous UPMresults, and must not be used until the screen has been replaced.

A 5.00 cm mark 1156 is scribed on the cylinder 1120 at a height k of5.00 cm (±0.05 cm) above the screen (not shown) attached to the bottom1148 of the cylinder 1120. This marks the fluid level to be maintainedduring the analysis. Maintenance of correct and constant fluid level(hydrostatic pressure) is critical for measurement accuracy.

A constant hydrostatic head reservoir 1014 is used to deliver saltsolution 1032 to the cylinder 1120 and to maintain the level of saltsolution 1032 at a height k of 5.00 cm above the screen (not shown)attached to the bottom 1148 of the cylinder 1120. The bottom 1034 of theair-intake tube 1010 is positioned so as to maintain the salt solution1032 level in the cylinder 1120 at the required 5.00 cm height k duringthe measurement, i.e., bottom 1034 of the air tube 1010 is inapproximately same plane 1038 as the 5.00 cm mark 1156 on the cylinder1120 as it sits on the support screen (not shown) on the ring stand 1040above the receiving vessel 1024. Proper height alignment of theair-intake tube 1010 and the 5.00 cm mark 1156 on the cylinder 1120 iscritical to the analysis. A suitable reservoir 1014 consists of a jar1030 containing: a horizontally oriented L-shaped delivery tube 1018 forfluid delivery, a vertically oriented open-ended tube 1010 for admittingair at a fixed height within the constant hydrostatic head reservoir1014, and a stoppered vent 1012 for re-filling the constant hydrostatichead reservoir 1014. Tube 1010 has an internal diameter of 12.5 mm±0.5mm. The delivery tube 1018, positioned near the bottom 1042 of theconstant hydrostatic head reservoir 1014, contains a stopcock 1020 forstarting/stopping the delivery of salt solution 1032. The outlet 1044 ofthe delivery tube 1018 is dimensioned to be inserted through the secondlid opening 1136 in the cylinder lid 1116, with its end positioned belowthe surface of the salt solution 1032 in the cylinder 1120 (after the5.00 cm height of the salt solution 1032 is attained in the cylinder1120). The air-intake tube 1010 is held in place with an o-ring collar(not shown). The constant hydrostatic head reservoir 1014 can bepositioned on a laboratory jack 1016 in order to adjust its heightrelative to that of the cylinder 1120. The components of the constanthydrostatic head reservoir 1014 are sized so as to rapidly fill thecylinder 1120 to the required height (i.e., hydrostatic head) andmaintain this height for the duration of the measurement. The constanthydrostatic head reservoir 1014 must be capable of delivering saltsolution 1032 at a flow rate of at least 3 g/sec for at least 10minutes.

The piston/cylinder assembly 1028 is positioned on a 16 mesh rigidstainless steel support screen (not shown) (or equivalent) which issupported on a ring stand 1040 or suitable alternative rigid stand. Thissupport screen (not shown) is sufficiently permeable so as to not impedesalt solution 1032 flow and rigid enough to support the stainless steelmesh cloth (not shown) preventing stretching. The support screen (notshown) should be flat and level to avoid tilting the piston/cylinderassembly 1028 during the test. The salt solution 1032 passing throughthe support screen (not shown) is collected in a receiving vessel 1024,positioned below (but not supporting) the support screen (not shown).The receiving vessel 1024 is positioned on the balance 1026 which isaccurate to at least 0.01 g. The digital output of the balance 1026 isconnected to a computerized data acquisition system (not shown).

Preparation of Reagents (not Illustrated)

Jayco Synthetic Urine (JSU) 1312 (see FIG. 13) is used for a swellingphase (see UPM Procedure below) and 0.118 M Sodium Chloride (NaCl)Solution is used for a flow phase (see UPM Procedure below). Thefollowing preparations are referred to a standard 1 liter volume. Forpreparation of volumes other than 1 liter, all quantities are scaledaccordingly.

JSU: A 1 L volumetric flask is filled with distilled water to 80% of itsvolume, and a magnetic stir bar is placed in the flask. Separately,using a weighing paper or beaker the following amounts of dryingredients are weighed to within ±0.01 g using an analytical balanceand are added quantitatively to the volumetric flask in the same orderas listed below. The solution is stirred on a suitable stir plate untilall the solids are dissolved, the stir bar is removed, and the solutiondiluted to 1 L volume with distilled water. A stir bar is againinserted, and the solution stirred on a stirring plate for a few minutesmore.

Quantities of salts to make 1 liter of Jayco Synthetic Urine:

-   -   Potassium Chloride (KCl) 2.00 g    -   Sodium Sulfate (Na₂SO4) 2.00 g    -   Ammonium dihydrogen phosphate (NH₄H₂PO₄) 0.85 g

Ammonium phosphate, dibasic ((NH₄)₂HPO₄) 0.15 g

-   -   Calcium Chloride (CaCl₂) 0.19 g—[or hydrated calcium chloride        (CaCl₂.2H₂O) 0.25 g]    -   Magnesium chloride (MgCl₂) 0.23 g—[or hydrated magnesium        chloride (MgCl₂.6H₂O) 0.50 g]

To make the preparation faster, each salt is completely dissolved beforeadding the next one. Jayco synthetic urine may be stored in a cleanglass container for 2 weeks. The solution should not be used if itbecomes cloudy. Shelf life in a clean plastic container is 10 days.

0.118 M Sodium Chloride (NaCl) Solution: 0.118 M Sodium Chloride is usedas salt solution 1032. Using a weighing paper or beaker 6.90 g (±0.01 g)of sodium chloride is weighed and quantitatively transferred into a 1 Lvolumetric flask; and the flask is filled to volume with distilledwater. A stir bar is added and the solution is mixed on a stirring plateuntil all the solids are dissolved.

Test Preparation

Using a solid reference cylinder weight (not shown) (40 mm diameter; 140mm height), a caliper gauge (not shown) (e.g., Mitotoyo Digimatic HeightGage) is set to read zero. This operation is conveniently performed on asmooth and level bench top 1046. The piston/cylinder assembly 1028without superabsorbent polymer particles is positioned under the calipergauge (not shown) and a reading, L₁, is recorded to the nearest 0.01 mm.

The constant hydrostatic head reservoir 1014 is filled with saltsolution 1032. The bottom 1034 of the air-intake tube 1010 is positionedso as to maintain the top part (not shown) of the liquid meniscus (notshown) in the cylinder 1120 at the 5.00 cm mark 1156 during themeasurement. Proper height alignment of the air-intake tube 1010 at the5.00 cm mark 1156 on the cylinder 1120 is critical to the analysis.

The receiving vessel 1024 is placed on the balance 1026 and the digitaloutput of the balance 1026 is connected to a computerized dataacquisition system (not shown). The ring stand 1040 with a 16 mesh rigidstainless steel support screen (not shown) is positioned above thereceiving vessel 1024. The 16 mesh screen (not shown) should besufficiently rigid to support the piston/cylinder assembly 1028 duringthe measurement. The support screen (not shown) must be flat and level.

UPM Procedure

1.5 g (±0.05 g) of superabsorbent polymer particles is weighed onto asuitable weighing paper or weighing aid using an analytical balance. Themoisture content of the superabsorbent polymer particles is measuredaccording to the Edana Moisture Content Test Method 430.1-99(“Superabsorbent materials—Polyacrylate superabsorbent powders—MoistureContent—weight loss upon heating” (February 99)). If the moisturecontent of the superabsorbent polymer particles is greater than 5%, thenthe superabsorbent polymer particles weight should be corrected formoisture (i.e., in that particular case the added superabsorbent polymerparticles should be 1.5 g on a dry-weight basis).

The empty cylinder 1120 is placed on a level benchtop 1046 and thesuperabsorbent polymer particles are quantitatively transferred into thecylinder 1120. The superabsorbent polymer particles are evenly dispersedon the screen (not shown) attached to the bottom 1148 of the cylinder1120 by gently shaking, rotating, and/or tapping the cylinder 1120. Itis important to have an even distribution of particles on the screen(not shown) attached to the bottom 1148 of the cylinder 1120 to obtainthe highest precision result. After the superabsorbent polymer particleshave been evenly distributed on the screen (not shown) attached to thebottom 1148 of the cylinder 1120 particles must not adhere to the innercylinder walls 1150. The piston shaft 1114 is inserted through the firstlid opening 1134, with the lip 1154 of the lid 1116 facing towards thepiston head 1118. The piston head 1118 is carefully inserted into thecylinder 1120 to a depth of a few centimeters. The lid 1116 is thenplaced onto the upper rim 1144 of the cylinder 1120 while taking care tokeep the piston head 1118 away from the superabsorbent polymerparticles. The lid 1116 and piston shaft 1126 are then carefully rotatedso as to align the third, fourth, fifth, and sixth linear index marksare then aligned. The piston head 1118 (via the piston shaft 1114) isthen gently lowered to rest on the dry superabsorbent polymer particles.The weight 1112 is positioned on the upper portion 1128 of the pistonshaft 1114 so that it rests on the shoulder 1124 such that the first andsecond linear index marks are aligned. Proper seating of the lid 1116prevents binding and assures an even distribution of the weight on thehydrogel layer 1318.

Swelling Phase: An 8 cm diameter fritted disc (7 mm thick; e.g.Chemglass Inc. # CG 201-51, coarse porosity) 1310 is saturated by addingexcess JSU 1312 to the fritted disc 1310 until the fritted disc 1310 issaturated. The saturated fritted disc 1310 is placed in a wideflat-bottomed Petri dish 1314 and JSU 1312 is added until it reaches thetop surface 1316 of the fritted disc 1310. The JSU height must notexceed the height of the fitted disc 1310.

The screen (not shown) attached to the bottom 1148 of the cylinder 1120is easily stretched. To prevent stretching, a sideways pressure isapplied on the piston shaft 1114, just above the lid 1116, with theindex finger while grasping the cylinder 1120 of the piston/cylinderassembly 1028. This “locks” the piston shaft 1114 in place against thelid 1116 so that the piston/cylinder assembly 1028 can be lifted withoutundue force being exerted on the screen (not shown).

The entire piston/cylinder assembly 1028 is lifted in this fashion andplaced on the fritted disc 1310 in the Petri dish 1314. JSU 1312 fromthe Petri dish 1314 passes through the fritted disc 1310 and is absorbedby the superabsorbent polymer particles (not shown) to form a hydrogellayer 1318. The JSU 1312 available in the Petri dish 1314 should beenough for all the swelling phase. If needed, more JSU 1312 may be addedto the Petri dish 1314 during the hydration period to keep the JSU 1312level at the top surface 1316 of the fritted disc 1310. After a periodof 60 minutes, the piston/cylinder assembly 1028 is removed from thefitted disc 1310, taking care to lock the piston shaft 1114 against thelid 1116 as described above and ensure the hydrogel layer 1318 does notlose JSU 1312 or take in air during this procedure. The piston/cylinderassembly 1028 is placed under the caliper gauge (not shown) and areading, L_(2,) is recorded to the nearest 0.01 mm. If the readingchanges with time, only the initial value is recorded. The thickness ofthe hydrogel layer 1318, L₀ is determined from L₂-L₁ to the nearest 0.1mm.

The piston/cylinder assembly 1028 is transferred to the support screen(not shown) attached to the ring support stand 1040 taking care to lockthe piston shaft 1114 in place against the lid 1116. The constanthydrostatic head reservoir 1014 is positioned such that the deliverytube 1018 is placed through the second lid opening 1136. The measurementis initiated in the following sequence:

-   -   a) The stopcock 1020 of the constant hydrostatic head reservoir        1014 is opened to permit the salt solution 1032 to reach the        5.00 cm mark 1156 on the cylinder 1120. This salt solution 1032        level should be obtained within 10 seconds of opening the        stopcock 1020.    -   b) Once 5.00 cm of salt solution 1032 is attained, the data        collection program is initiated.

With the aid of a computer (not shown) attached to the balance 1026, thequantity of salt solution 1032 passing through the hydrogel layer 1318is recorded at intervals of 20 seconds for a time period of 10 minutes.At the end of 10 minutes, the stopcock 1020 on the constant hydrostatichead reservoir 1014 is closed.

The data from 60 seconds to the end of the experiment are used in theUPM calculation. The data collected prior to 60 seconds are not includedin the calculation. The flow rate F_(s) (in g/s) is the slope of alinear least-squares fit to a graph of the weight of salt solution 1032collected (in grams) as a function of time (in seconds) from 60 secondsto 600 seconds.

The Urine Permeability Measurement (Q) of the hydrogel layer 1318 iscalculated using the following equation:

Q=[F _(g) ×L ₀ ]/[ρ×A×ΔP],

where F_(g) is the flow rate in g/sec determined from regressionanalysis of the flow rate results, L₀ is the initial thickness of thehydrogel layer 1318 in cm, ρ is the density of the salt solution 1032 ingm/cm³. A (from the equation above) is the area of the hydrogel layer1318 in cm², ΔP is the hydrostatic pressure in dyne/cm², and the UrinePermeability Measurement, Q, is in units of cm³ sec/gm. The average ofthree determinations should be reported.

FSR Test Method

This method determines the speed of superabsorbent polymer particles,especially polymeric hydrogelling particles, such as cross-linkedpoly-acrylates to swell in 0.9% Saline (aqueous 0.9 mass % NaClsolution). The measurement principle is to allow superabsorbent polymerparticles to absorb a known amount of fluid, and the time taken toabsorb the fluid is measured. The result is then expressed in grams ofabsorbed fluid per gram of material per second. All testing is conductedat 23±2° C.

Four grams of a representative sample of the superabsorbent polymerparticles is dried in an uncovered 5 cm diameter Petri dish in a vacuumchamber at 23±2° C. and 0.01 torr or lower for 48 hours prior tomeasurement.

About 1 g (+/−0.1 g) of the test specimen is removed from the vacuumchamber and immediately weighed to an accuracy of 0.001 g into a 25 mlbeaker, which has 32 to 34 mm inside diameter, and 50 mm height. Thematerial is evenly spread over the bottom. 20 g of 0.9% Saline areweighed to an accuracy of +/−0.01 g in a 50 ml beaker, and are thenpoured carefully but quickly into the beaker containing the testmaterial. A timer is started immediately upon the liquid contacting thematerial. The beaker is not moved or agitated during swelling.

The timer is stopped, and the time recorded to the nearest second (ormore accurately if appropriate), when the last part of undisturbed fluidis reached by the swelling particles. In order to increase thereproducibility of the determination of the end point, the liquidsurface can be illuminated by a small lamp without heating the surfaceby that lamp. The beaker is re-weighed to determine the actually pickedup liquid to within ±0.1 g.

The free-swell rate is calculated by dividing the weight ofsuperabsorbent polymer particles by the amount of actually picked upliquid, and dividing the result by the time required for this pick up,and is expressed in “g/g/s”. Three measurements are performed and theresults averaged to obtain the FSR value in g/g/s, reported to 3significant figures.

Flat Acquisition Test Method

This method determines the acquisition times of a baby diaper typicallydesignated for wearers having a weight in the range of 8 to 13 kg±20%(such as Pampers Active Fit size 4 or other Pampers baby diapers size 4,Huggies baby diapers size 4 or baby diapers size 4 of most othertradenames).

Apparatus

The test apparatus is shown in FIG. 14 and comprises a trough 1411 madeof polycarbonate (e.g. Lexan®) nominally 12.5 mm (0.5 inch) inthickness. The trough 1411 comprises a rectilinear horizontal base 1412having a length of 508 mm (20.0 inches), and a width of 152 mm (6.0inches). Two rectilinear vertical sides 1413 64 mm (2.5 inches) tall×508mm (20 inches) in length are affixed to the long edges of the base 1412to form a U-shaped trough 1411 having a length of 508 mm (20.0 inches),an internal width of 152 mm (6.0 inches), and an internal depth of 51 mm(2.0 inches). The front and back ends of the trough 1411 are notenclosed.

A slab of open-cell polyurethane foam 1414 with dimensions 508×152×25 mmis wrapped in polyethylene film and placed in the bottom of the trough1411 in such a way that the edges of the foam 1414 and the trough 1411are aligned, and the upper surface of the polyethylene film is smoothand free of seams, wrinkles or imperfections. The polyurethane foam 1414has a compressive modulus of 0.48 psi. A reference line is drawn acrossthe width of the upper surface of the polyethylene cover 152 mm (6.0inches) from one end (the front edge) parallel to the transversecenterline using an indelible marker.

A rectilinear polycarbonate top plate 1415 has a nominal thickness of12.5 mm (0.5 inch), a length of 508 mm (20.0 inches), and a width of 146mm (5.75 inches). A 51 mm (2.0 inch) diameter hole is bored in thecenter of the top plate 1415 (i.e. the center of the hole is located atthe intersection of the longitudinal and transverse axes of the uppersurface of the top plate 1415). A polycarbonate cylinder 1416 with anoutside diameter of 51 mm (2.0 inches), an internal diameter of 37.5 mm(1.5 inches) and a height of 102 mm (4.0 inches) is glued into the holein the top plate 1415 so that the bottom edge of the cylinder 1416 isflush with the lower surface of the top plate 1415 and the cylinder 1416protrudes vertically 89 mm (3.5 inches) above the upper surface of thetop plate 1415, and the seam between the cylinder 1416 and the top plate1415 is watertight. An annular recess 1417 with a height of 2 mm and adiameter of 44.5 mm (1.75 inches) is machined into the bottom internaledge of the cylinder 1416. Two 1 mm diameter holes are drilled at a 45°angle to the upper surface of the top plate 1415 so that the holesintersect the inner surface of the cylinder 1416 immediately above therecess 1417 and are at opposite sides of the cylinder 1416 (i.e. 180°apart). Two stainless steel wires 1418 having a diameter of 1 mm areglued into the holes in a watertight fashion so that one end of eachwire is flush with the inner cylinder wall and the other end protrudesfrom the upper surface of the top plate 1415. These wires are referredto as electrodes hereinbelow. A reference line is scribed across thewidth of the top plate 1415 152 mm (6.0 inches) from the front edgeparallel to the transverse centerline. The top plate 1415/cylinder 1416assembly has a weight of approximately 1180 grams.

Two steel weights each weighing 9.0 Kg and measuring 146 mm (5.75inches) wide, 76 mm (3.0 inches) deep, and approximately 100 mm (4inches tall) are also required.

Procedure:

All testing is carried out at 23±2° C. and 35±15% relative humidity.

The polycarbonate trough 1411 containing the wrapped foam slab 1414 isplaced on a suitable flat horizontal surface. A disposable absorbentproduct is removed from its packaging and the cuff elastics are cut atsuitable intervals to allow the product to lay flat. The product isweighed to within ±0.1 grams on a suitable top-loading balance thenplaced on the covered foam slab 1414 in the acquisition apparatus withthe front waist edge of the product aligned with the reference mark onthe polyethylene cover. The product is centered along the longitudinalcenterline of the apparatus with the topsheet (body-side) of the productfacing upwards and the rear waist edge toward the rear end of the foamslab 1414. The top plate 1415 is placed on top of the product with theprotruding cylinder facing upwards. The scribed reference line isaligned with the front waist edge of the product and the rear end of thetop plate 1415 is aligned with the rear edge of the foam slab 1414. Thetwo 9.0 Kg weights are then gently placed onto the top plate 1415 sothat the width of each weight is parallel to the tranverse centerline ofthe top plate, and each weight is 83 mm (3.25 inches) from the front orrear edge of the top plate 1415.

A suitable electrical circuit is connected to the two electrodes todetect the presence of an electrically conductive fluid between them.

A suitable pump; e.g. Model 7520-00 supplied by Cole Parmer Instruments,Chicago, USA, or equivalent; is set up to discharge a 0.9 mass % aqueoussolution of sodium chloride through a flexible plastic tube having aninternal diameter of 4.8 mm ( 3/16 inch), e.g Tygon® R-3603 orequivalent. The end portion of the tube is clamped vertically so that itis centered within the cylinder 1416 attached to the top plate 1415 withthe discharge end of the tube facing downwards and located 50 mm (2inches) below the upper edge of the cylinder 1416. The pump is operatedvia a timer and is pre-calibrated to discharge a gush of 75.0 ml of the0.9% saline solution at a rate of 15 ml/sec.

The pump is activated and a timer started immediately upon activation.The pump delivers 75 mL of 0.9% NaCl solution to the cylinder 1416 at arate of 15 ml/sec, then stops. As test fluid is introduced to thecylinder 1416, it typically builds up on top of the absorbent structureto some extent. This fluid completes an electrical circuit between thetwo electrodes in the cylinder. After the gush has been delivered, themeniscus of the solution drops as the fluid is absorbed into thestructure. When the electrical circuit is broken due to the absence offree fluid between the electrodes in the cylinder, the time is noted.

The acquisition time for a particular gush is the time interval betweenactivation of the pump for that gush, and the point at which theelectrical circuit is broken.

Four gushes are delivered to the product in this fashion; each gush is75 ml and is delivered at 15 ml/sec. The time interval between thebeginning of each gush is 300 seconds.

The acquisition time for four gushes is recorded. Three products aretested in this fashion and the average gush time for each of therespective gushes (first through fourth) is calculated.

EXAMPLES

Absorbent structures according to the present disclosure have beenprepared to compare their properties with the properties of absorbentstructures of the prior art. All the tested absorbent structurescomprise superabsorbent polymer particles which are sandwiched betweentwo substrate layers made of nonwoven material. For the data given inTable 1, all the samples have been taken from an absorbent core. Thesamples correspond to the portion of the absorbent core of an absorbentarticle (size 4) which is centered on the longitudinal centerline of thearticle, at a distance of 152 mm from the front waist edge of thearticle. In the portion of the absorbent core where the samples aretaken, the absorbent structures of examples 1 and 2 and comparativeexamples 1 and 2 have the same structure. They only differ with regardto the superabsorbent polymer particles which have been used. For thedata given in Table 2, the whole absorbent structures of Example 2 andComparative Examples 1 and 2 have the same structure and only differwith regard to the superabsorbent polymer particles which have beenused.

Comparative Example 1

An absorbent structure comprising the same superabsorbent polymerparticles as the ones which are used in Pampers Active Fit diaperscommercially available in the UK in August 2010 has been prepared. Thesesuperabsorbent polymer particles are generally made according to US2009/0275470 A1. It should be noted that the superabsorbent polymerparticles may be isolated from the commercially available Pampers ActiveFit diapers as described in European patent application no 10154618.2entitled “Method of separating superabsorbent polymer particles from asolidified thermoplastic composition comprising polymers”.

The Standard particle size distribution of the superabsorbent polymerparticles is of 45 to 710 μm with a maximum of 1% below 45 μm and amaximum of 1% above 710 μm.

Comparative Example 2

300 g of superabsorbent polymer particles have been prepared accordingto comparative example 11 disclosed in the PCT patent application WO2010/095427 A1 entitled “Polyacrylic acid-based water-absorbing resinpowder and method for producing the same”. An absorbent structurecomprising such superabsorbent polymer particles has been prepared.

Example 1

4000 kg of superabsorbent polymer particles of comparative example 1have been sieved over a AISI 304 standard 300 μm stainless steel wiremesh in a riddle sieve equipment with a capacity of about 100-150 kg perhours yielding to 750 kg of superabsorbent polymer particles with amedium diameter (D50) of about 180-200 μm and a particle sizedistribution of 45 to 300 μm with a maximum of 3% below 45 μm and amaximum of 3% above 300 μm. An absorbent structure comprising suchsuperabsorbent polymer particles has been prepared

Example 2

300 g of superabsorbent polymer particles have been prepared accordingto example 9 disclosed in the PCT patent application WO 2010/095427 A1entitled “Polyacrylic acid-based water-absorbing resin powder and methodfor producing the same”. An absorbent structure comprising suchsuperabsorbent polymer particles has been prepared.

Several parameters of the absorbent structures of examples 1 and 2 andof the comparative examples 1 and 2 have been measured: the time toreach an uptake of 20 g/g (T20), the uptake at 20 min (U20), the time toreach an uptake of 80% of U20 (T80%), the effective permeability at 20minutes (K20) and the transient gel blocking index (Kmin/K20) have beenmeasured according to K(t) Test Method set out above. The UPM (UrinePermeability Measurement) of the superabsorbent polymer particles of theabsorbent structures of Examples 1 and 2 and of the comparative examples1 and 2 has been measured according to the UPM Test method set outabove. The CRC (Centrifuge Retention Capacity) of the superabsorbentpolymer particles has been measured according to EDANA method WSP241.2-05.

FIGS. 18A and 18B represent the uptake in g/g as a function of time forthe absorbent structures of the comparative examples 1 and 2 vs.examples 1 and 2 as measured according to the K(t) Test Method set outabove.

The different values for the measured parameters are summarized in Table1 below.

TABLE 1 UPM T20 U20 T80% Kmin/ (1 × 10⁻⁷ CRC Examples (s) (g/g) (g/g)K20 (cm²) K20 (cm3 · s)/g) (g/g) Comparative 495 23.8 414 3.43 · 10⁻⁸0.92 98 26.5 Example 1 Comparative 477 24.1 410 4.75 · 10⁻⁸ 0.96 11027.3 Example 2 Example 1 200 23.9 177  2.8 · 10⁻⁸ 0.72 66 24.1 Example 2344 25.0 343 3.13 · 10⁻⁸ 0.86 100 27.7

As can be seen from FIGS. 18A and 18B and from Table 1, the times toreach an uptake of 20 g/g (T20) as measured according to the K(t) testmethod for the absorbent structures made according to examples 1 and 2are significantly lower than for the absorbent structures made accordingto the comparative examples 1 and 2. Therefore, these absorbentstructures are able to rapidly absorb liquid even in the dry stage, i.e.upon initial exposure to liquid.

As can also be seen from Table 1 is that superabsorbent polymerparticles having a high permeability at equilibrium (high UPM value)such as the superabsorbent polymer particles of the absorbent structuresof comparative examples 1 and 2 do not automatically lead to a high T20value for the absorbent structure comprising such superabsorbent polymerparticles which means that the permeability at equilibrium of thesuperabsorbent polymer particles is not a reliable criterion in order toselect the absorbent structures which are able to rapidly absorb liquidupon initial exposure to liquid.

-   -   Acquisition times of diapers comprising an absorbent structure        which comprises the superabsorbent polymer particles of        comparative examples 1 or 2 vs. diapers comprising an absorbent        structure which comprises the superabsorbent polymer particles        according to the present disclosure.

Acquisition times of Pampers Active Fit size 4 diapers commerciallyavailable in the UK in August 2010 have been measured according to theFlat Acquisition Test Method set out above. These diapers comprise anabsorbent core which comprises the superabsorbent polymer particles ofthe comparative example 1. Acquisition times of the same diapers whereinthe absorbent core has been replaced by an absorbent core with the samestructure but wherein the superabsorbent polymer particles have beenreplaced by the superabsorbent polymer particles of comparative example2 or example 2 have been measured according to the Flat acquisition testmethod set out above. The absorbent cores of all the diapers have a drythickness at the crotch point of the diaper of 1.7 mm as measuredaccording to the Caliper Measurement Test Method set out above. Thevalues obtained for the acquisition times of all samples are summarizedin Table 2 below.

TABLE 2 Comparative Comparative Samples Example 1 Example 2 Example 2Acquisition time of 1st gush 30 28 26 (75 mL) in s

As can be seen from Table 2 above, the acquisition times of the firstgush for diapers comprising an absorbent core which comprisessuperabsorbent polymer particles according to comparative examples 1 or2 are higher than the acquisition time of the first gush for the samediaper wherein the superabsorbent polymer particles have been replacedby the superabsorbent polymer particles of Example 2.

Hence, absorbent articles according to the present invention, namelyabsorbent articles comprising an absorbent structure wherein one or moreportion(s) of the absorbent structure comprise(s) at least 90% ofsuperabsorbent polymer particles and require(s) a time to reach anuptake of 20 g/g (T20) of less than 440 s as measured according to theK(t) test method have improved absorption properties, especially at thefirst gush, i.e. when the article starts to be wetted.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application, is hereby incorporated herein by reference in itsentirety unless expressly excluded or otherwise limited. The citation ofany document is not an admission that it is prior art with respect toany invention disclosed or claimed herein or that it alone, or in anycombination with any other reference or references, teaches, suggests,or discloses any such invention. Further, to the extent that any meaningor definition of a term in this document conflicts any meaning ordefinition of the same term in a document incorporated by reference, themeaning or definition assigned to that term in this document shallgovern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. An absorbent article comprising an absorbentstructure, the absorbent article being divided into three portions: afront portion, a back portion and a crotch portion disposed between thefront portion and the back portion, the absorbent structure comprisingan absorbent core, the absorbent core having a dry thickness at a crotchpoint of the article of from about 0.2 to about 5 mm, wherein one ormore portion(s) of the absorbent structure comprise(s) at least about90% by weight of superabsorbent polymer particles and require(s) a timeto reach an uptake of about 20 g/g (T20) of less than about 440 s asmeasured according to the K(t) test method.
 2. The absorbent articleaccording to claim 1, wherein one of the one or more portion(s) of theabsorbent structure is centered on the center of the front portion ofthe article and/or one of the one or more portion(s) of the absorbentstructure is centered on the crotch point of the article.
 3. Theabsorbent article according to claim 1, wherein the absorbent articlefurther comprises a topsheet and a backsheet, wherein the absorbent coreis sandwiched between the topsheet and the backsheet.
 4. The absorbentarticle according to claim 1, wherein the one or more portion(s) of theabsorbent structure have an effective permeability at about 20 minutes(K20) of at least about 2.9·10⁻⁸ cm² as measured according to the K(t)test method.
 5. The absorbent article according to claim 1, wherein theuptake of the one or more portion(s) of the absorbent structure at about20 min (U20) is of at least about 24 g/g as measured according to theK(t) test method.
 6. The absorbent article according to claim 1, whereinthe absorbent core is airfelt free.
 7. The absorbent article accordingto claim 1, wherein the absorbent core comprises an average amount ofsuperabsorbent polymer particles per surface area of the absorbent coreof from about 200 to about 900 g/m² in the crotch portion of thearticle.
 8. The absorbent article according to claim 1, wherein theabsorbent article has an acquisition time for the first gush of lessthan about 27 s as measured according to the Flat acquisition testmethod.
 9. The absorbent article according to claim 1, wherein thesuperabsorbent polymer particles are comprised in the absorbent core,such that the superabsorbent polymer particles are deposited between afirst and a second substrate layer, with the first substrate layerfacing towards the backsheet and the second substrate layer facingtowards the topsheet.
 10. The absorbent article according to claim 9,wherein the superabsorbent polymer particles are immobilized bythermoplastic adhesive material.
 11. The absorbent article according toclaim 1, wherein the absorbent core comprises a first substrate layer,at least a portion of the superabsorbent polymer particles beingdeposited on the first substrate layer and thermoplastic adhesivematerial immobilizing the superabsorbent polymer particles.
 12. Theabsorbent article according to claim 11, wherein the absorbent corefurther comprises a second substrate layer, at least a portion of thesuperabsorbent polymer particles being deposited on the second substratelayer and thermoplastic adhesive material immobilizing thesuperabsorbent polymer particles, the first and second substrate layersbeing combined together such that at least a portion of thethermoplastic adhesive material of the first substrate layer contacts atleast a portion of the thermoplastic adhesive material of the secondsubstrate layer.
 13. The absorbent article according to claim 10,wherein the thermoplastic adhesive material forms a fibrous network overthe superabsorbent polymer particles.
 14. The absorbent articleaccording to claim 1, wherein at least one of the one or more portion(s)of the absorbent structure has a surface area of about 30 cm² or more,15. The absorbent article according to claim 14, wherein at least one ofthe one or more portion(s) of the absorbent structure having a surfacearea of about 30 cm² or more encompasses a circular area.